Bio 1

Question 1

1.3 Explain why
phospholipids form
bilayers in water,
with reference to
hydrophilic
phosphate heads
and two
hydrophobic
hydrocarbon tails.

Answer 1

The membrane is composed of phospholipids with
hydrophilic heads and hydrophobic tails, and
proteins are embedded between these
phospholipids
Phospholipids form bilayers in water due to the
amphipathic properties of phospholipid
molecules.
Cholesterol in mammalian membranes reduces
membrane fluidity and permeability to some
solutes.

Question 2

1.5 Explain the
origin of eukaryotic
cells, and evidences
present

Answer 2

With endosymbiosis a larger cell takes in a smaller
cell by endocytosis, so the smaller cell is inside a
vesicle in the cytoplasm of the larger cell.
A cell that respired anaerobically took in a
bacterium that respired aerobically, supplying
both itself and the larger cell with energy in the
form of ATP.
Evidences:
Membrane bounded organelles (mitochondria
and chloroplasts)
Antibiotics (susceptible, indicating that organelles
may have bacterial origins)
DNA
Division occurs in a fission like process
Ribosomes (contains 70s ribosomes)

Question 3

1.3 List at least four
functions (with
example) of
membrane bound
proteins.

Answer 3

Structure:
-channel proteins that open and close
-carrier proteins that change shape to transport
big molecules
-peripheral proteins
-glycoproteins
Function:
1. Receptor proteins communicate signals
between the cells internal and external
environments (ie. Hormone receptor); connect
and join cells
2. Enzymes catalyze reactions (ie. ATP synthase);
localizes metabolic pathways; used as a catalyst
3. Transport proteins move ions and molecules
across the membrane (ie. Aquaporin transports
water) via facilitated diffusion and active transport
(using AT to change shape)
4. Recognition - cellular identification (MHC
proteins and antigens)
5. Adhesion molecules ancho the cell to other
cells (ie. Cadherin)Recognition proteins identify
the cell type (ie. Major histo-compatibility
complex proteins)
6. Anchorage - attachment points for
cytoskeleton & extracellular mix

Question 4

1.3 Describe the
function of
cholesterol
molecules in the
cell membrane

Answer 4

Cholesterol acts as a requlator of membrane
fluidity (which is the viscosity of the cell
membrane)
-at high temperatures, it stabilizes the membrane
and raises the melting point
-at low temperatures it prevents phospholipids
from packing too close together which would
lead to stiffening (allows the kink to form)
The membrane fluidity affects how permeable the
structure is to solutes:
-too fluid –> too much permeability
-too stiff -> not enough permeability
-cholesterol functions to immobilize the outer
surface of the membrane, reducing fluidity.
-it makes the membrane less permeable to very
small water-soluble molecules that would
otherwise freelv cross.
-functions to separate phospholipid tails and so
prevent crystallization of the membrane
-helps secure peripheral proteins by forming high
density lipid rafts capable of anchoring the
protein

Question 5

1.2 Name two
organelles which
are involved in the
secretion of
enzymes from a salivary gland cell.

Answer 5

The Endoplasmic Reticulum and Golgi apparatus.
The rE synthesizes proteins for secretion, while
the Golgi apparatus packages it and carries it
using vesicles to the plasma membrane for
secretion.

Question 6

1.3 Define
amphipathic and
outline the
amphipathic
properties of
phospholipids.

Answer 6

Amphipathic: having both hydrophilic and
hydrophobic parts
Phospholipids are amphipathic as they have both
hydrophilic, which is their head and hydrophobic
parts which is their tail.

Question 7

1.2 Prokaryotes
divide through
which process?

Answer 7

Prokaryotes divide asexually through binary
fission.
The bacterial chromosome is replicated so there
are two identical copies, and cytokinesis occurs to
split apart to form two identical cells.

Question 8

1.4 What are the
four types of
molecules which
need to be
transported across
the membrane?

Answer 8

small molecules (oxygen)
larger molecules (glucose)
small ions (sodium ions)
large proteins

Question 9

1.3 What are the
three main types of
protein in
phospholipids?

Answer 9

glycoprotein, integral protein, and peripheral
protein

Question 10

1.5 What evidence
do we have to
support that cells
come from pre-
existing cells?

Answer 10

Examples of growth, be it of tissue, an organism,
or population.
2. Genetic code, universal of 64 codes that
produce the same amino acid in translation,
regardless of the organism.
3. Viruses are produced from simpler subunits, but
they are not cells.

Question 11

1.3 What type of
substances do cell
membranes allow
to enter the cell?

Answer 11

lipid soluble substances; oxygen, carbon dioxide,
steroids

Question 12

1.6 Contrast
cytokinesis in plant
and animal cells.

Answer 12

Animal cell:
-animal cells do not have to form a cell wall.
-a cleavage furrow is formed during cytokinesis in
animal cells.
Plant cell:
-plant cells must create new cell wall between
the daughter cells;
-carbohydrate-rich vesicles form in a row at the
center of the cell
-vesicles fuse together and an early cell plate
begins to form within the middle of the cell
-cell plate extends outwards and fuses with the
cell wall, creating a new cell wall

Question 13

1.5 Explain the
origin of the first
cells.

Answer 13

Spontaneous generation was not possible, so
living cells can be formed on Earth today except
division of pre-existing cells.
The universality of the genetic code suggests
strongly that all life evolved from the same
original cells.
**that there are some minor variations that are
likely to have accrued since the common origin of
life on Earth.
The non-living synthesis of simple organic
molecules has been demonstrated by the Miller-
Urey experiment.
-recreated the postulated conditions of pre-biotic
Earth using a closed system of flasks and tubes
Conclusion:
1. Non-living materials synthesizes simple organic
molecules like sugars and amino acids.
2. These organic molecules are assembled into
polymers.
3. These polymers form, and can self-replicate
(enabling inheritance)
4. Membranes are formed to package the organic
molecules.

Question 14

1.3 Skill: Drawing of
the fluid mosaic
model and explain.

Answer 14

States that the phospholipid bilayer behaves more
like a liquid than a solid.
Fluid because the phospholipids and proteins
move side to side like a liquid; can quickly
reassemble themselves even though it breaks
Mosaic because when viewed from above, the
scattered protein molecules look like a mosaic;
constructed of different molecules.

Question 15

1.6 Describe the
process of a cell
cycle.

Answer 15

The cell cycle starts with the process of
interphase, which consists of three stages.
1. In Gl phase, the cell grows in size with
cytoplasms and organelles produced.
2. In S phase, DNA is replicated.
3. G2 is an extension stage of Gl.
The goal is to prepare for the process of mitosis
coming up next.
Mitosis consists of four phases.
1. In prophase, the chromosomes become visible
because DNA supercoils and the chromosomes
are condensed, and they move to the opposite
sides of the cell.
2. In metaphase, the chromosomes line up in the
middle and is held together by the centromere,
connecting to the microtubule spindle fibers.

3. In anaphase, the microtubule spindle fibers
   contracts, and pull the sister chromatids to the
   opposite sides of the cell, and chromosomes are
   formed.
4. In telephase, the chromosome sets arrive at the
   poles, the chromosomes decondense and the
   spindle fibre disappears. Nuclear membrane
   reform around each chromosome set.
   Cytokinesis happen concurrently with telephase
   to separate the cell membrane.

Question 16

1.3 Describe the
observations and
conclusions drawn
by Davson and
Danielli in
discovering the
structure of cell
membranes.

Answer 16

This plasma membrane model is known as the
“Sandwich Model”
-describes a phospholipid bilayer that lies
between two layers of globular proteins.
Analysis of evidence:
-in high electron micrographs, membranes
appeared as two dark lines separated by a lighter
band.
-seemed to fit the Davson Danielli model, as
proteins usually appear darker than phospholipids
in electron micrographs.
-therefore it was thought that there were 2 layers
of protein on the two sides of the membrane.
-electron micrograph shows membranes both at
the surfaces of cells and around vesicles with the
appearance that seemed to back up the Davson
Danielli model.
It was the first model that attempted to describe
the position of proteins within the lipid bilayer
found in membranes, but what was wrong was
their proposal of two layers of protein flanking a
central phospholipid bilayer.

Question 17

1.3 Skill: Describe
conclusions about
cell membrane
structure drawn
from various
research methods,
which falsified
Davson-Danielli’s
sandwich mode.

Answer 17

Freeze Fracturing:
-cells are rapidly frozen and then fractured.
-fracture occurs along lines of weakness,
including the centre of membranes.
-globular structures throughout the membrane
were interpreted as transmembrane proteins.
-reveals an irregular rough surface inside the
phospholipid bilayers
*transmembrane proteins were not accounted for
by the Darson-Danielli model of the cell
membrane
Later analysis:
-interpreted as being transmembrane proteins,
demonstrating that proteins were not solely
localised to the outside of the membrane
structure
fluorescent antibody tagging:
-Frye and Edidin (1970) fused two cells labeled
with different membrane-bound fluorescent tags
and watched as the two protein populations
mixed.
-the revealed color shows that membrane
proteins are liquid like and are free to move
-when cells are fused together, the color mixes,
showing that the plasma membrane is not a static
layer

-showed that membrane proteins can move
around within the bilayer, they are not locked in
place.
Solubility of proteins:
-membrane proteins were discovered to be
insoluble in water (hydrophobic)
-such proteins would not be able to form a
uniform and continuous laver around the outer
surface of a membrane
Improvements in biochemical techniques allowed
proteins to be extracted from membranes. The
proteins were found to be:
-varied in size, unlike the type of protein that
would form continuous layers on the outside of
the membrane as Davson and Danielli had
proposed.
-hydrophobic on at least part of their surface,
unlike the completely hydrophilic proteins on the
outside of the membrane as Davson and Danielli
had proposed.

Question 18

1.3 Evaluate the
Davson-Danielli
Model.

Answer 18

1. It assumed all membranes were of a uniform
   thickness and would have a constant lipid-protein
   ratio
2. It assumed all membranes would have
   symmetrical internal and external surfaces (i.e. not
   bifacial)
3. It did not account for the permeability of
   certain substances (did not recognise the need
   for hydrophilic pores)
4. The temperatures at which membranes
   solidified did not correlate with those expected
   under the proposed model

Question 19

1.6 Describe the
process of
interphase.

Answer 19

The cell cycle starts with the process of
interphase, which consists of three stages.
1. In Gl phase, the cell grows in size with
cytoplasms and organelles produced.
2. In S phase, DNA is replicated.
3. G2 is an extension stage of Gl.
The goal is to prepare for the process of mitosis
coming up next.
Purpose of interphase is to:
1. Metabolic reactions (e.g. respiration to produce
ATP)
2. Cell growth (increase of volume in cytoplasm)
3. Protein synthesis (proteins and enzymes)
4. Organelles (produced, number increases)
5. Nutrients (vital cellular materials must be present)
6. DNA is replicated (in S phase, prepare for
mitosis)

Question 20

1.3 Describe the
newly proposed
Singer-Nicholson
Model.

Answer 20

It is called the fluid mosaic model, and proteins
were embedded within the lipid bilayer rather
than existing as separate layers.
-membranes are fluid, meaning they can change
shape and flow (1.4.U2)
-proteins are dispersed throughout the
membrane, leaving many portions of the lipid
bare and exposed to the extra- and intracellular
environments.
-proteins are peripheral and integral to the lipid
bilayer.
-integral proteins have hydrophobic regions.

Question 21

1.6 Use
epidemiological
case study
information to
outline the
relationships
between smoking
and cancer.

Answer 21

-cigarette smoke contains over 4,000 chemical
compounds, over 60 of which are known to be
carcinogenic
-there appears to be a strong positive correlation
between the frequency of smoking and the
development of cancer
-the risk of lung cancer is strongly correlated with
smoking, with -90% of lung cancers attributable to
tobacco use
-smoking also increases the risk of over a dozen
other cancers, including mouth, stomach, liver,
panceas and bowel

Question 22

1.6 What are the
other factors that
may increase the
chance of gene
mutation?

Answer 22

1. Some people has a vast number of cells, which
   increases the chances of genetic mutation.
2. People with a longer life span (older people)

Question 23

1.4 Explain how
particles move
across membrane.

Answer 23

Particles move across membranes by simple
diffusion, facilitated diffusion, osmosis and active
transport.
simple diffusion:
-the passive movement o particles rom a region o
higher concentration to a region o lower
concentration
-a result of the random motion o particles.
facilitated diffusion:
-channel proteins allow one type o substance to
pass through.
-cells can control whether substances pass
through their plasma membranes, by the types o
channel protein
-high -> low concentration
active transport:
-requires ATP
-against concentration gradient
osmosis:

the direction in which water moves is due to the
concentration of solutes
-the passive movement of water molecules from
a region of lower solute concentration to a
region of higher solute concentration
The fluidity of membranes allows materials to be
taken into cells by endocytosis or released by
exocytosis. Vesicles move materials within cells.
Exocytosis:
1) vesicles bud of rER carrying proteins to Golgi
apparatus
2) vesicles bud of Golgi apparatus
3) vesicles fuse with the plasma membrane, and
are expelled
Exocytosis may remove both waste products
and useful substances.
Exocytosis depends on the flexibility of the
plasma membrane.
*Exocytosis requires energy.
Endocytosis:
1) part of the plasma membrane is pulled inwards
2) vesicle pinches of, substance becomes
enclosed

Question 24

1.4 What are the
three types of
endocytosis?

Answer 24

phagocytosis, pinocytosis, receptor-mediated
endocytosis

Question 25

1.4 Outline factors
that regulate the
rate of diffusion.

Answer 25

concentration of the diffusing molecule
o greater the difference in concentration between
two areas, the greater the rate of diffusion
• temperature
o greater the temperature, the greater the rate of
diffusion because temperature increases the rate
of molecular movement
• pressure
o greater the pressure, the greater the rate of
diffusion because pressure increases the rate of
molecular movement
• surface area
o the one with more surface area will diffuse
faster
• length of diffusion path
o shorter length will be faster
• molecular size
o larger substances have greater resistance

Question 26

1.6 Explain the role
of cyclin and cyclin-
CDK complexes in
controlling the cell
cycle

Answer 26

-cyclins are regulatory proteins that control cell
cycle events; phase specific; activate CDKs
-cyclins activate cyclin dependent kinases (CDKs),
which control cell cycle processes through
phosphorylation
-cyclin-dependent kinases are activated by the
process of phosphorylation by a CDK-activating
kinase (CAK)
-a cyclin and CDK form a complex, the complex
will bind to a target protein and modify it via
phosphorylation
-the phosphorylated target protein will trigger
some specific event within the cell cycle (e.g
centrosome duplication, etc.)
-after the event has occurred, the cyclin degraded and the CDK is rendered inactive again
Controlling the cell cycle:
-cyclin concentrations need to be tightly
regulated to ensure that tasks are performed at
the correct time and that the cell only moves on
to the next stage of the cycle when it is
appropriate.
-cyclins bind to enzymes called cyclin-dependent
kinases
-these kinases then become active and attach
phosphate groups to other proteins in the cell.
-cyclin levels will peak when their target protein is required for function and remain at lower levels
at all other times.
-unless these cyclins reach a threshold
concentration, the cell does not progress to the
next stage o the cell cycle.

Question 27

1.4 What are the
adaptions in
Biology for better
diffusion rate?

Answer 27

1. Maintaining a large gradient
2. Reducing the length of diffusion path
   -membranes are thin
   -folded membrane, higher SA:Vol
3. Maximizing surface are for absorption

Question 28

1.6 Explain factors
that are involved in
the development of
primary and
secondary tumours.

Answer 28

Mutagens, oncogenes and metastasis are involved
in the development of primary and secondary
tumours.
mutagens -> mutation in DNA -› oncogenes
**mutations have to occur in several oncogenes in
the same cell for control to be lost.
Most cancers are caused by mutations to two
basic classes of qenes - proto-oncogenes and
tumor suppressor genes
Proto-oncogenes:
code for proteins that stimulate the cell cycle and
promote cell growth and proliferation
Tumor suppressor:
genes code for proteins that repress cell cycle
progression and promote apoptosis (death of
cells)
These two types of genes are good originally, but
when mutated or subjected to increased
expression it becomes a cancer-causing oncogene.
primary tumours -> metastasis -> secondary
tumours

Question 29

1.4 Describe the
structure and
function of sodium-
potassium pumps
for active transport
and potassium
channels for
facilitated diffusion
in axons.

Answer 29

Facilitated Diffusion in Axons:
The axons of neurons contain potassium channels
that reused during an action potential.
Potassium channels in axons are voltage gated;
-closed when the axon is polarized
-open in response to depolarization of the axon
membrane to enable facilitated diffusion of K+ in
the axon and Na+ out of the cell.
-narrow diameter; so only one substance can
move at once
-chemical properties; specific to a potassium ions
-can move in either directions but depends on the
concentration gradient
Potassium channels only remain open for a very
short time before a globular sub-unit blocks the
pore.
Sodium-potassium pumps for active transport:
-sodium and potassium are pumped in opposite
directions
-shape change in the pump is solely controlled by
the ion concentration gradient.
-one ATP provides enough energy
-DNA donates a phosphate group to the pump.
-pump two potassium ions in

-three sodium ions out of the cell
-two binding sites for K+ ions and three for Na+
ions

Question 30

1.4 Describe the
process of
secondary active
transport.

Answer 30

Indirect coupling transport with another molecule
that is moving along its electrochemical gradient.
e.g. Glucose uptake in the kidneys is an example
of symport, as its movement is coupled to the
parallel transport of sodium.

Question 31

1.1 How are
specialized tissues
developed?

Answer 31

Specialized tissues can develop by cell
differentiation in multicellular organisms, from the
totipotent stem cells.
Differentiation involves the expression of some
genes and not others in a cell’s genome.
The capacity of stem cells to divide and
differentiate along different pathways is
necessary in embryonic development.

Question 32

1.1 What are the
three types of stem
cells?

Answer 32

embryonic stem cells
umbilical cord stem cells
bone marrow stem cells

Question 33

1.1 State the cell
theory.

Answer 33

a. living things are composed of cells;
b. cells are the basic/smallest unit of life;
c. cells come from pre-existing cells;
Do not accept cells are the “smallest organisms”
Do not accept “cells are the building blocks” of
life on its own

Question 34

1.1 Outline the
functional
characteristics of
life.

Answer 34

MR H GREN
Metabolism
-sum of all chemical reactions in a cell
Response
Homeostasis
-living organisms keep their internal environments
within a certain range, despite changes in external
environment
Growth
-growth: increase in size and mass of an organism
-development: transformation of organism
throughout its lifespan (e.g. metamorphosis)
Reproduction
Excretion
Nutrition

Question 35

1.11. Explain the
importance of
surface area to
volume ratio as a
factor limiting cell
size. [7 marks]

Answer 35

as volume of a cell increases, the ratio of its
surface area to volume decreases;
food/oxygen enters through the surface of
cells;wastes leave through the surface of cells;
the rate of substance crossing the membrane
depends on surface area;
more metabolic activity in a larger cell means
more food and oxygen required;
large volume means longer diffusion time; (large
volume) means more wastes produced;
excess heat generated will not be lost efficiently
(with low surface area to volume ratio);
eventually surface area can no longer serve the
requirements of the cell;
this critical ratio stimulates mitosis;
(thus) the size of the cell is reduced and kept within size limits

Question 36

1.1 Distinguish a
property only
multicellular
organisms have.

Answer 36

Multicellular organisms have properties that
emerge from the interaction of their cellular
components.
Organisms consisting of only one cell carry out all
functions of life in that cell, therefore do not have
emergent properties.

Question 37

1.1 Describe features
of atypical
examples to the cell
theory.

Answer 37

striated muscle: long thin cell and has multiple
nuclei
giant algae: large, up to 7 cm length
aseptate fungal hyphae: hyphae separated into
cells by septa, and has a continuous cytoplasm
along the length of hyphae
-not made of clearly defined individual cells
-long branching single cell structures

Question 38

1.1 Outline the cause
and symptoms of
Stargardt’s disease,
and explain how
stem cells are used
in the treatment of
Stargardt’s disease..

Answer 38

Stargardt’s disease:
-due to a recessive mutation of a gene called
ABCA4.
-caused by a recessive mutation of a broken
protein that doesn’t transport in and out of the
cell
-photoreceptive cells in the retina degenerate
-as a mutation in the ABCA4 gene causes the
accumulation of lipofuscin, which causes the
impairment of the macula and the death of the RPE cells.
-photoreceptors are affected as well, as their
survival depends on the RPE cells.
-stem cells are used to replenish retina cells for
visually impaired individuals
-retina cells derived from embryonic stem cells
are injected into the eyes
-the cells attach to the retina and improve vision
without harmful side effects.

Question 39

1.1 Investigate the
functions of life in
Paramecium and
one named
photosynthetic
unicellular
organism.

Answer 39

Paramecium and scenedesmus.
Use MR H GREN
**they are both unicellular EUKARYOTES
Paramecium:
-metabolism: food particles are enclosed within
small vacuoles that contain enzymes for digestion;
cytoplasm contains enzymes that act as a catalyst
for the metabolic
-responsiveness: surrounded by small hairs called
cilia which allow it to move
-homeostasis: essential gases (e.g. 02) enter and
exit (e.g. CO2) the cell via diffusion; contractile
vacuoles fill up with water, the water then passes
out through the plasma membrane, this maintans
the water levels inside the cell relatively constant
-reproduction: divide asexually (binary fission)
although horizontal gene transfer can occur via
conjugation; nucleus of the cell can divide to
producethe extra nuclei that are needed when
the cell reproduces.
-excretion: solid wastes are removed via an anal
pore, while liquid wastes are pumped out via
contractile vacoules
-nutrition: engulf food via a specialised
membranous feeding groove called a cytosol
-growth: nutrients from digestion produce enough
energy for growth
Scenedesmus:
-metabolism: chlorophyll pigments allow organic
molecules to be produced via photosynthesis
-reproduction: internal asexual division of the
parent cell
-responsiveness: scenedesmus may exist as
unicells or form colonies for protection
-excretion/nutrition: scenedesmus exchange
gases and other essential materials via diffusion.
-Metabolic reactions take place in the cytoplasm,
with enzymes present to speed them up.

Question 40

1.2 Distinguish
prokaryotes and
eukaryotes

Answer 40

Prokaryotes have a simple cell structure without
compartmentalization, while Eukaryotes have a
compartmentalized cell structure.
In eukaryotes, enzymes and substrates used in a
process can be concentrated in a small area, with
pH and other conditions at optimum levels and
with no other enzymes that might disrupt the
process.

Question 41

1.1 Which
microscope
achieves the highest
magnification and
greatest resolution?

Answer 41

Electron microscopes have a much higher
resolution than light microscopes

Question 42

1.5 Describe how
Pasteur’s
experiments
provided
convincing
evidence to falsify
the concept of
spontaneous
generation.

Answer 42

spontaneous generation is life appearing from
nothing / from non-living / cells only come from
pre-existing cells/life
b. broth/culture medium (for bacteria) (used/
placed) in flasks
C. broth boiled/sterilized «in some flasks» to kill
microbes
d. no clouding/signs of bacterial growth/
reproduction / microbes did not appear «in flasks
of boiled broth»
Allow bacteria or organisms instead of microbes.
e. after necks of flasks were snapped boiled broth became cloudy/growth of microbes
f. because microbes from the air contaminated the
«boiled» broth
g. curved necks allowed indirect exposure to air
but prevented entry of microbes
h. no organisms appeared spontaneously in
curved necks

Question 43

1.1 Discuss the ethics
of the therapeutic
use of stem cells
from specially
created embryos,
from the umbilical
cord blood of a
new-born baby and
from an adult’s own
tissues.

Answer 43

For:
-use of stem cells for the health and quality of life
of patients suffering from otherwise incurable
conditions may be greatly improved
Against:
-source of stem cells: use of an adult’s own stem
cells or cells from an adult volunteer.
**stem cells taken from specially created embryos
are more controversial.
-embryo is a human life even at the earliest stage
and if the embryo dies as a result of the
procedure it is immoral
Counter Arguments: Against
-they are balls of cells that have yet to develop
the essential features of a human life
-lack a nervous system so do not feel pain or
suffer in other ways
-large numbers of embryos produced by IVF are
never
implanted and do not get the chance of life

Question 44

1.1 State the formula
of calculating the
magnification of
drawings and the
actual size of
structures and
ultrastructures
shown in drawings
or micrographs; and
the conversion units
for calculation.

Answer 44

TE AM
I: image size
A: actual size
M: magnification
*cells actual size measured in micrometers
10^-3 to convert from mm to micrometer

Question 45

Skill: Drawing of the
ultrastructure of
prokaryotic cells
based on electron
micrographs.
State the features
that will need to be drawn

Answer 45

cell wall
plasma membrane
flagella
pilli
nucleoid region (with naked DNA)
cytoplasm
70s ribosomes

Question 46

1.2 Skill: Drawing of
the ultrastructure of
eukaryotic cells
based on electron
micrographs.
State the features
that will need to be
drawn

Answer 46

cell wall (only for plant cell)
plasma membrane
cytoplasm
80s ribosomes
Single Membrane:
Rough endoplasmic reticulum
smooth endoplasmic reticulum
golgi apparatus
Lysosomes
Vesicles and vacuoles
Double Membrane:
Nucleus
Mitochondrion
Chloroplast (plant cell)

Question 47

1.4 Application:
Explain why tissues
or organs to be
used in medical
procedures must be
bathed in a solution
with the same
osmolarity.

Answer 47

Osmosis can cause cells in human tissues or
organs to swell up and burst, or to shrink due to
gain or loss of water by osmosis.
-A solution of salts called isotonic saline is used
for some procedures.
-Donor organs are surrounded by isotonic slush
when they are being transported, with the low
temperatures helping to keep them in a healthy
state.

Question 48

1.4 Skill: Estimation
of osmolarity in
tissues by bathing
samples in
hypotonic and
hypertonic
solutions

Answer 48

the osmolarity of a solution is the number of
moles of solute particles per unit volume of
solution.
greater concentration = higher osmolarity
water = zero osmolarity
4x15zt
-lose water when placed in hypertonic solutions
-gain water when placed in hypotonic solutions
Water loss or gain may be determined by
weighing the sample before and after bathing in
solution
Accuracy in osmosis experiments:
-the volume of water used for making solutions should be measured with a volumetric flask
-the initial and final mass of tissue samples should
be measured with the same electronic balance
that is accurate to 0.01 grams (10 mg).

Question 49

1.6 Define mitosis.

Answer 49

Mitosis is division of the nucleus into two
genetically identical daughter nuclei.

Question 50

1.6 Describe the
events that occur
during mitosis.

Answer 50

sequence of stages is prophase > metaphase >
anaphase > telophase;
chromosomes condense/supercoil/become
shorter and fatter in prophase;
spindle microtubules grow (from poles to
equator) in prophase/metaphase;
nuclear membrane breaks down in prophase/
metaphase;
spindle microtubules attach to the centromeres/
chromosomes in metaphase;
chromosomes line up at equator in metaphase;
centromeres divide / (paired) chromatids
separate / chromosomes separate into two
chromatids in metaphase/anaphase; (sister)
chromatids/chromosomes pulled to opposite
poles in anaphase;

spindle microtubules disappear in telophase;
nuclear membrane reforms around
chromosomes/chromatids in telophase:
chromosomes/chromatids decondense in
telophase;

Question 51

1.6 Skill:
Determination of a
mitotic index from a
micrograph.
State the formula
for the calculation
of mitotic index.

Answer 51

-the ratio between the number of cells in mitosis
in a tissue and the total number of observed cells
-mitotic index = # cells in mitosis/total # of cells
The mitotic index is used by doctors to predict
how rapidly a tumour will grow and therefore
what treatment is needed.

Question 52

11 Outline evidence
that supports the
cell theory.

Answer 52

From 17th century on, biologists examined tissues
from both plants and animals, and saw that every
specimen contained one or more cells
1) Antone van Leeuwenhoek 1675
Unicellular organism - ‘animalcules’; live cells
2) Matias Schleiden 1838
Suggests all plants are made of cells
3) Robert Hooke 1665
Cork cells; with microscope; dead cells; Hooke’s discovery led to the understanding of cells as the
smallest units of life-the foundation of cell
theory.
4) Louis Pasteur 1859
Disproved spontaneous generation
Also discovered pasteurization
5) Schwann
Found that all animals are made of cells
6) Virchow
Cells come from pre-existing cells
-supported Louis and Pasteur’s experiment
supported that idea

Question 53

1.1 Outline the
activities occurring
in the volume and at
the surface of the
cell.

Answer 53

Volume: cell volume is primarily composed of
cytoplasm.
-many metabolic reactions are occurring in the
cytoplasm
-the metabolic reactions require nutrients and
may produce waste.
SA is proportional to the rate of exchange of
materials.
Surface area: the cell surface area is the cell
membrane
-regulates the transport of molecules into and out
of the cell
-through which nutrients and gases more into the
cell and metabolic wastes leave the cell

Question 54

1.1 Explain the
benefits and
limitations of using
cubes to model the
surface area and
volume of a cell.

Answer 54

Cubes are often used to model limitations of cell
size. Cubes can be manipulated, visualized and
easily measured.
-however, cells are not cubic in shape.
-cells are more difficult to manipulate and
measure because of their microscopic size.
-luckily, the relationship between SA and volume
is the same in both cubes and cells.

Question 55

1.1 Explain why cells
are often limited in
size by the SA:V
ratio.

Answer 55

Small cells = large SA : Volume ratio
-small volume: fewer metabolic nutrients and
wastes to be transported through the cell
membrane
-molecules have shorter distance to diffuse within
the cell
-large SA: more cell membrane for transportation
of materials in and out of the cell
-since the amount of surface area (membrane)
relative to the amount of volume (cytoplasm)
decrease in larger cells, the cell will not have a
large enough surface area (membrane) to move
nutrients into or wastes out of the cell.
-within cells, molecules have larger diffusion
distance
-larger cells would require more nutrients and
create more waste in the metabolic reactions
occurring in the cytoplasm.
-as the cell grows, the SA is no longer sufficient to
serve the needs of cell (from the large volume)
-a decreasing SA: Volume ratio will stimulate cell
division through mitosis or binary fission

Question 56

1.1 List three
adaptations of cells
that maximize the
SA: volume ratio.

Answer 56

Thin, flattened shape: RBC, type I pneumocyte in
alveoli, epithelial cell forming a capillary tube
Microvilli: small intestine epithelial cells, cell of
kidney proximal convoluted tube
Roots of plants that are long and branched with
microroots; epidermis cell with root hair

Long extensions: neurons; increase the flow of
ions?

Question 57

1.1 Define and
provide an example
of unicellular and
multicellular
organism.

Answer 57

Unicellular organism: an organism composed of a
single cell.
e.g paramecium, amoeba and chlamydomonas
Multicellular organism: an organism composed of
multiple cells.

e.q. a turtle, an oak tree and an eagle

Question 58

1.1 Define “emergent property” and provide examples at different hierarchical levels of life.

Answer 58

Emergent properties are properties/characteristics/abilities that only arise from the interaction of the component parts of a structure to produce entirely new aggregate functions.

structure Emergent property
-heart cell characteristic of life heart tissue can
synchronize contractions
-heart organ can pump blood
-circulatory system can deliver blood throughout
the body
-organism can use blood for interconnected
functions

Question 59

1.1 Define tissue.

Answer 59

A tissue is a group of cells that specialize in the
same way to perform the same function.

Question 60

1.1 Outline the
benefits of cell
specialization in a
multicellular
organism.

Answer 60

-cells can be more efficient in their role, by
focusing on one task and saving energy by not
performing other tasks
-can have a specialized structure and metabolism
-as they focus on only one or a few tasks, thev
evolve faster in that particular task
-enzymes can developed to carry out role more
efficiently

Question 61

1.1 Define
differentiation.

Answer 61

Differentiation is the development of specialized
structures and functions in cells through the
expression of certain genes but not others
(selective gene expression).

Question 62

1.1 Describe the
relationship
between cell
differentiation and
gene expression.

Answer 62

Differentiation involves the expression of some
genes and not others in a cell’s genome.
-all cells in a multicellular organism contain the
same genes but different cells will express
different genes
-to express a gene means to “switch it on” so that
the protein (or other gene product) is made (due
to differences in gene expression)
-gene expression is the process by which
information from a gene is used in the synthesis of
functional gene product (protein)
-differentiation in gene expression is regulated by
proteins that bind to specific base sequences in
DNAzygote and embryo.

Question 63

1.1 Define zygote
and embryo.

Answer 63

Zygote: a single diploid cell resulting from the
fusion of two haploid gametes; a fertilized ovum
(early embryo cell, approximately:)
Embryo: an unborn or unhatched offspring in the
process of development; early stage of human
development; a zygote undergoes mitosis to
become an embryo

Question 64

1.1 Describe the
characteristics of
stem cells that make
them potentially
useful in medicine.

Answer 64

Stem cells can divide repeatedly:
-useful for treatment of tissues that need to
replace cells that have been killed or damaged.
Stem cells are not differentiated:
-they havn’t “turned off” genes so they can still
differentiate to produce different cell types
(stem cells) have/retain the capacity to divide;
can be used to produce cell cultures/large
number of identical cells;
can be used to repair/replace damaged/lost
cells/tissue; (stem cells) are undifferentiated /
have not yet differentiated/specialized;
can differentiate/specialize in different ways / are
pluripotent/totipotent;
can be used to form a variety of different tissues /
form organs;
used in medical research;
used in treatment of (named) disease;

Question 65

1.1 Contrast the
characteristics of
embryonic,
umbilical cord and
adult somatic stem
cells.

Answer 65

Embryonic stem cells:
-can differentiate into any body cell (pluripotent);
almost unlimited growth potential.
-more risk of becoming tumour cells than adult
stem cells, including teratomas that contain
different tissue types
-less chance of genetic damage due to the
accumulation of mutations than with adult stem
cells
-likely to be genetically different from an adult
patient receiving the tissue.
-removal of cells from the embryo kills it, unless
onlv one or two cells are taken.
Umbilical stem cells:
-can only differentiate into blood cells
(multipotent)
-easily obtained and stored.
-commercial collection and storage services
already available.
-fully compatible with the tissues of the adult that
grows from the baby, so no rejection problems
Occur.
-limited capacity to differentiate into different cell
types -only naturally develop into blood cells, but
research may lead to production of other types.
-limited quantities of stem cells from one baby’s
cord.
-the umbilical cord is discarded whether or not stem cells are taken from it.

Adult somatic stem cells:
-found in bone marrow, skin and liver; limited
differentiation ability (multipotent)
-difficult to obtain as there are very few of them
and they are buried deep in tissues.
-less growth potential than embryonic stem cells.
-less chance of malignant tumours developing
than from embryonic stem cells.
-limited capacity to differentiate into different cell
types
-fully compatible with the adult’s tissues, so
rejection problems do not occur.
-removal of stem cells does not kill the adult from
which the cells are taken.

Question 66

1.1 Define totipotent,
multipotent and
pluripotent.

Answer 66

Totipotent: can become any body cell plus
placenta. The zygote is totipotent
Pluripotent: can become any body cell (but not
placenta.
e.g. blastoycst is (I.C.M) pluripotent
Multipotent: have partially differentiated but can
still become multiple, related cell types (umbilical
cord stem cells and adult stem cells)

Question 67

11 Outline the cause
of leukemia, and
explain how stem
cells are used in the
treatment of
leukemia

Answer 67

-leukemia is a cancer that results from an
accumulation of mutations leading to
uncontrolled division of the cells that create white
blood cells.
-increase levels of abnormal WBCs
-main symptoms include tiredness and or anemia,
repeated infections as well as increased bruising
and bleeding.
-cancer of bone marrow, abnormally producing
dis functioning white blood cells
-person with leukemia is given chemotherapy,
which kills the cancer cells.
-inject healthy stem cells (HSC stem cells)
harvested from bone marrow, peripheral blood,
or umbilical cord to differentiate into WBCs
-the stem cells establish themselves, divide and
start to produce blood cells.

Question 68

1.1 Define
magnification.

Answer 68

How much larger an object appears compared to
its real size.

Question 69

1.1 State why the
magnification of a
drawing or
micrograph is not
the same as the
magnification of the
microscope.

Answer 69

We draw structures much larger than we view
them under a microscope. So what we see, even
magnified, is much smaller than what we show in a
drawing.

Question 70

1.1 Define “trend”
and “discrepancy.”

Answer 70

Trend: a general direction in which something is
developing or changing
Discrepancy: an illogical or surprising lack of
compatibility or similarity between two or more
facts

Question 71

1.1 Explain why
“trends and
discrepancies” are
useful in scientific
study.

Answer 71

Trends: lead to the development of scientific
theories and allow for predictions to be made
Discrepancies: can lead to new discoveries

Question 72

1.1 List features that
would be
considered a
“trend” related to
the cell theory.

Answer 72

All cells have a cell membrane
All cells have genetic material
All cells have ribosomes
All cells have cytoplasm
All cells have an energy release system

Question 73

1.1 Explain why
biological research
must take ethical
issues into
consideration.

Answer 73

Biological research is a human endeavor and as
such will lead to people having different opinions
about what is ethical and should be permitted.
The opinions must be considered while deciding
what is best for the collective good.

Question 74

1.2 Outline the major
differences
between
prokaryotic and
eukaryotic cells.

Answer 74

PROKARYOTE:
-tiny (0.2-2um)
-nucleoid (no nuclear membrane)
-no organelles
-flagella rotates
-cell wall of peptidoglycan
-smaller 70s ribosomes
-DNA is circular, naked (no nucleus)
-has plasmids
-asexual cell division
EUKARYOTE:
-bigger (10-100um)
-true nucleus
-organelles present
-flagella moves laterally
-cell wall of cellulose (plants) or chitin (fungus)
-larger, 80s ribosomes
-DNA is linear, with histones
-does not have plasmidsAsexual or sexual
reproduction

Question 75

1.2 List the functions
of the following
structures of a
prokaryotic cell.

Answer 75

Cell membrane: responsible for regulating what
materials move into and out of the cell
Nucleoid (DNA region for prokaryotes): genetic
material (DNA) circular, naked DNA
Plasmid: genetic material often with genes for
antibiotic resistance
Cytoplasm (cytosol): gel like fluid substance, site
of many metabolic reactions
Ribosome: (70s) build proteins during translation
Cell wall (some): outer peptidoglycan covering
that protects and provides shape
Pili(some): hair like structures that help the cell
attach to surfaces
Capsule(some): helps cell maintain moisture and
adhere to surfaces. Protects cell from other
organisms.
Flagella (some): long extensions used in cell
locomotion

Question 76

1.2 State the
meaning and
advantages of
eukaryotic cells
being
“compartmentalized”

Answer 76

Compartmentalization: the presence of
membrane bound partitions (aka organelles)
inside the eukaryotic cell.
These compartments allow for:
-specialization for specific functions without
interference from other cell functions.
e.g. lysosomes can digest cell debris without
digesting the cell itself.
-allows molecules needed for a function (for
example enzymes or ions) to reach a higher
concentration than if all molecules were diluted in
the cytoplasm.
e.g. the mitochondria accumulates a large H+
concentration which is used to fuel ATP synthesis
-optimal conditions for pH (other conditions)
-toxic substances can be kept inside membranes
-cell can have a lot of one type of organelle to
be better in a specific function

Question 77

12 Define asexual
reproduction.

Answer 77

Asexual reproduction creates offspring from a
single organism. The offspring are genetic clones
of that parent.

Question 78

12 Outline the steps
of binary fission.

Answer 78

The circular (nucleoid) DNA is copied in response
to a replication signal
The two DNA loops attach to the membrane
The (new nucleoid) DNA attaches to the cell
membrane close to the original.
The cell membrane (and wall if present) grow,
causing the cell to elongate and the DNA
molecules to move apart from each other.
The cell membrane (and wall if present) pinch
inwards, creating two genetically identical cells

Question 79

1.2 Define
resolution.

Answer 79

Smallest interval distinguishable by the
microscope.
Shortest distance between two points that can be
distinguished.
The larger the distance, the lower the resolution.
The shorter the distance, the higher the resolution
(vou can see more things in one look)

Question 80

1.2 State the
function of an
exocrine gland cell
and describe the
functions of it
organelles.

Answer 80

Exocrine gland cells synthesize molecules (often
protein enzymes) for secretion from the cell into
an external space (for example a, salivary gland)
Plasma (cell) membrane: regulates passage of
materials into and out of the cell
Nucleus: contains the genetic code (used to make
proteins) and contains the nucleolus (where
ribosomes are synthesized)
Mitochondria: location of cellular respiration used
to make ATP. The ATP can then be used to fuel
the cells protein synthesis, transport and secretion
processes.
Golgi apparatus: modifies proteins before they
are used, stored or released from the cell
Lysosome: contains digestive enzymes that can be
used to break apart cellular debris and waste
Vesicles: transport materials within the cell and
out of the cell via exocytosis.
Endoplasmic reticulum: ribosome on the rough ER
synthesis proteins which are then moved through
the ER and packed into vesicles for transport
Peroxisome: Store enzymes that require oxygen
(oxidative enzymes).
Contain enzymes that break down fatty acids,
amino acids and alcohol, resulting in the
production of the toxic substance, hydrogen
peroxide.

Also contain high levels of the enzyme catalase
which breaks down the hydrogen peroxide into
harmless products, 02 and H20.
*presence of large amounts of rough
endoplasmic reticulum and many Golgi
apparatuses shows that the main function of this
exocrine gland cells is to synthesize and secrete
proteins, presumably the enzymes in pancreatic
juice.
-cells secrete digestive enzymes into a duct, to
the small intestine where food are digested.

Question 81

1.2 State the
function of a
palisade mesophyll
cell and describe
the functions of its
organelles.

Answer 81

Palisade mesophyll cells are found on the upper
surface of a leaf and have the primary job of
performing photosynthesis
Cell wall: provides structural rigidity and support
Plasma (cell) membrane: regulating passage of
materials into and out of the cell
Chloroplast: location of photosynthesis
Vacuole: water filled sac that helps maintain cell
turgidity
Nucleus: holds DNA, the genetic code for making
proteins. Also has the nucleolus where ribosomes
are synthesized.

Mitochondria: site of cellular respiration, where
glucose chemical is converted to ATP chemical
energy
many chloroplasts and a large vacuole,
indicating that the function of this cell was
photosynthesis.
-in a cylindrical shape
*it is the cell type that carries out most
photosynthesis.

Question 82

1.2 Explain why the
ultrastructure of
prokaryotic cells
must be based on
electron
micrographs.

Answer 82

“ultra structures” are small structures of/in a
biological specimen that are too little to see with
a light microscope

Question 83

1.2 Explain why cells
with different
functions will have
different structures.

Answer 83

Cells have different organelles depending on the
primary function of the cell type. This allows cells
to specialize for a specific task which can lead to
increased complexity of the entire organism.

Question 84

12 With reference
to a specific
example, explain
how an
improvement in
apparatus allowed
for greater
understanding of
cell structure.

Answer 84

-from the change of light microscope to electron
microscope allows us to see the structures better

Question 85

1.3 Define
hydrophilic and
hydrophobic.

Answer 85

Hydrophilic: having a tendency to mix with,
dissolve in, or be wetted by water.
Hydrophobic: tending to repel or fail to mix with
water

Question 86

1.3 State the primary
function of the cell
membrane.

Answer 86

The cell membrane is semi-permeable and
controls the movement of substances in and out
of cells

Question 87

1.3 Contrast the
structure of integral
and peripheral
proteins.

Answer 87

Peripheral proteins sit on the surface or have
small sections that dip in the bilayer.
-monotopic
-hydrophilic
-indirectly or loosely attached to the surface of
the cell membrane
-may dip slightly into the lipid bilayer.
-attach to the membrane via by reversible
electrostatic interactions or hydrogen bonds with
phospholipid heads at the membrane surface or
with another membrane protein.

Integral proteins have:
-large sections embedded in the hydrophobic
middle of the membrane.
-some integral proteins are “transmembrane”
meaning they cross the membrane
-most integral proteins span the entire
phospholipid bilayer.
-polytopic
-amphipathic
-have hydrophobic amino acids that interact with
hydrophobic fatty acid tails of the membrane
phospholipids (1.3.U1), thus anchoring the protein
to the membrane

Question 88

1.3 Contrast the two
types of transport
proteins.

Answer 88

Channel proteins are used for passive transport of
molecules often shapes like pores/tunnels. Pump
proteins are used for active transport of
molecules.

Question 89

1.3 Describe the
structural
placement of
cholesterol within
the cell membrane

Answer 89

Cholesterol fits between phospholipids in the cell
membrane, with its hydroxyl (OH) group by the
heads and the hydrophilic rings by the fatty acid
tails.
Cholesterol has a unique structure consisting of:
-a hydroxyl group linked at one end
-four linked hydrocarbon rings
-a hydrocarbon tail linked to the other end

Question 90

1.3 Draw and label
the structure of
membranes.

Answer 90

Draw and label the structure of membranes.
Include:
Phospholipid bilayer
Integral proteins shown spanning the membrane
Peripheral proteins on membrane surface
Protein channels with a pore
Glycoproteins with a carbohydrate side chain
Cholesterol between phospholipids in the
hydrophobic region

Question 91

1.3 Describe
conclusions about
cell membrane
structure drawn
from improvements
in techniques for
determining the structure of
membrane proteins.

Answer 91

-improvements in tools and techniques allowed
scientists to extract membrane proteins and
determine their chemical and physical properties.
-membrane proteins were found to be carried in
shape and size.
-some proteins were hydrophobic (or partially
hydrophobic)
-these findings did not match the model proposed
by Darson and Danielli, in which proteins would
be relatively uniform in shape and hydrophilic in
nature.

Question 92

1.3 Compare the
Davson-Danielli
model of
membrane structure
with the Singer-
Nicolson model

Answer 92

Singer and Nicolson proposed a membrane
model that incorporated evidence about
membrane proteins that did not comply with the
Davson Danielli model. Rather than having
proteins on the surface of the phospholipids,
Singer-Nicolson propoed a model in which
proteins were embedded within and through the
membrane, called the Fluid-Mosaic Model.

Davson Danielle proposed that cell membranes
are static/cannot move
Singer-Nicolson proposed that cell membrane is
fluid

Question 93

1.3 Explain what
models are and
their purposes in
science.

Answer 93

Models are conceptual representations used to
explain and predict phenomena.

Question 94

1.3 Describe why
the understanding
of cell membrane
structure has
changed over time.

Answer 94

As tools and technologies advance, our
understanding of biological structures and
functions also improves. Techniques such as
freeze-fracture, cell fusion, fluorescent antibody
tagging and protein extraction enabled scientists
to gain a more accurate understanding of the
structure of cell membrane proteins.

Question 95

1.4 Describe simple
diffusion.

Answer 95

-the movement of substances across a membrane
without the assistance of channel proteins.
-tendency of particles to distribute themselves
evenly throughout the available space as a result
of continuous random motion of the particles
-in circumstances where there is an uneven
distribution of particles in different regions, results
in net movement of particles from a region of
high concentration to a region of lower
concentration of that particle.
-if there is a difference in the concentration of a
substance across a cell membrane, particles of
that substance will tend to move across the
membrane down the concentration gradient.

Question 96

1.4 Explain two
examples of simple
diffusion of
molecules into and out of cells.

Answer 96

gas exchange by diffusion in lung alveoli cells
diffusion of molecules across the villi to be
absorbed in the blood

Question 97

1.4 Describe
facilitated diffusion.

Answer 97

the passage of molecules or ions down their
gradient across a biological membrane with the
assistance of specific transmembrane transport
proteins
it does not require energy

Question 98

1.4 Describe one
example of
facilitated diffusion
through a protein
channel.

Answer 98

The CFTR channel moves chloride ions from high
concentration inside the cell to areas of lower
concentration outside the cell

Question 99

1.4 Define osmosis.

Answer 99

The tendency of molecules of a solvent to pass
through a semipermeable membrane from a less
concentrated solution into a more concentration

Question 100

1.4 Compare active
transport and
passive transport.

Answer 100

Active
-requires energy
-input “against the concentration gradient
-from low to high
Passive
-does not require energy
- “with” the concentration gradient
-from high to low

Question 101

1.4 Explain one
example of active
transport of
molecules into and
out of cells through
protein pumps

Answer 101

hydrogen pump for co-transport of sucrose in
phloem loading in plants

Question 102

1.4 Describe the
fluid properties of
the cell membrane
and vesicles.

Answer 102

a. (labelled) phospholipid consisting of head and
two tails;
b. head is glycerol and phosphate;
C. tails are fatty acid chains;
d. head hydrophilic and tails hydrophobic;
e. hydrophilic molecules/heads attracted to/
soluble in water;
f. hydrophobic molecules/tails not attracted to
water but attracted to each other;
g. (properties of phospholipids leads to)
formation of double layer in water;
h. stability in double layer because heads on outer edge are attracted to water and tails are
attracted to each other in middle;
i. phospholipid bilayer in fluid/flexible state
because of attraction of non-polar tails to each
other;
j. (fluidity) allows membranes to change shape/
vesicles to form or fuse with membrane/ (fluidity)
allows cells to divide;
k. non-polar amino acid side chains attracted to
(hydrophobic) tails;
Marks may be earned using suitable labelled/
annotated diagrams illustrating the points given
above.

Question 103

1.4 Explain vesicle
formation via
endocytosis.

Answer 103

a. (plasma) membrane encloses/engulfs solid
particles/droplets of fluid/molecules;
b. fluidity of the membrane allows endocytosis;
C. (plasma) membrane forms pit/forms
indentation/pulled inwards/invaginates;
d. membrane pinches off /seals back on itself/
edges fuse;
e. vesicle/vacuole formed;
f. inside of plasma membrane becomes outside of
vesicle membrane / converse;
q. vesicle breaks away from plasma membrane/
moves into cytoplasm;
h. active process / endocytosis/vesicle formation
requires energy;
Accept any of the above points clearly described
in an annotated diagram.

Question 104

1.4 Outline two
examples of
materials brought
into the cell via
endocytosis.

Answer 104

-white blood cells can engulf bacteria during
infection (phagocytosis)
-single cell organisms like amoeba can engulf
bacteria as food

Question 105

1.4 Outline how
vesicles are used to
transport materials
secreted by a cell.

Answer 105

vesicles formed from rER transport proteins to
Golgi apparatus;
these vesicles fuse with membranes of Golgi
apparatus;
proteins are processed as they move through
Golgi apparatus;
(transport) vesicles bud off/leave Golgi
apparatus;
vesicles move through cytoplasm;
(vesicles) fuse with plasma membrane;
contents released to outside of cell / exocytosis;
cells use vesicles to secrete substances such as
hormones/digestive enzymes/other appropriate
example;
vesicles may contain cell products other than
proteins;
Credit drawings which fully explain the points
above.

Question 106

1.4 Outline two
examples of
materials released
from a cell via
exocytosis.

Answer 106

-secretion of neurotransmitter proteins to send
signal between neurons
-secretion of saliva from salivary glands in the
mouth
-hormones

Question 107

1.4 List two reasons
for vesicle
movement.

Answer 107

movement of substances within the cell
importing and exporting substances in and out of
the cell

Question 108

1.4 Outline how
phospholipids and
membrane bound
proteins are
synthesized and
transported to the
cell membrane

Answer 108

-phospholipids are synthesized in the ER.
-the phospholipids become part of the ER
membrane.
-when a transport vesicle buds off the ER, the
newly made phospholipid will be part of the
vesicle.
-there may also be proteins (made at a ribosome
on the ER) than embed in the vesicle.
-as the vesicle moves through the cell towards
the Golgi and then towards the cell membrane,
the new phospholipid and protein are also
transported.
-when the vesicle fuses with the cell membrane,
the new phospholipid and protein will become
part of the cell membrane.

Question 109

1.4 Describe the
structure of the
sodium-potassium
pump.

Answer 109

-integral membrane protein
-had binding sites for three sodium ions, two
potassium ions and an inorganic phosphate group
(which comes from ATP).

Question 110

1.4 Describe the
role of the sodium-
potassium pump in
maintaining
neuronal resting
potential.

Answer 110

-functions to move sodium and potassium ions in
response to the change in voltage
-the axons of nerve cells transmit electrical
impulses by translocating ions to create a voltage
difference across the membrane
-at rest, the sodium-potassium pump expels
sodium ions from the nerve cell, while potassium
ions are accumulated within
-when the neuron fires, these ions swap locations
via facilitated diffusion via sodium and potassium
channels

Question 111

1.4 Outline steps of
sodium-potassium
pump action.

Answer 111

three sodium ions bind to intracellular sites on
the sodium-potassium pump
2. a phosphate group is transferred to the pump
via the hydrolysis of ATP
3. the pump undergoes a conformational change,
translocating sodium across the membrane
4. the conformational change exposes two
potassium binding sites on the extracellular
surface of the pump
5. the phosphate group is released which causes
the pump to return to its original conformation
6. this translocates the potassium across the
membrane, completing the ion exchange

Question 112

1.4 Describe how
organelles of the
endomembrane
system function
together to
produce and
secrete proteins
(rough ER, smooth
ER, Golgi and
vesicles).

Answer 112

1. In the nucleus, transcription of DNA, creating
   mRNA.
2. Translation of mRNA at a ribosome on the
   Rough ER, creating a protein
3. Packaging of the protein into a transport
   vesicle.
4. Transport of the protein inside the vesicle to
   the Golgi.
5. Modification of the protein within the Golgi.
6. Packaging of the protein into a secretory
   vesicle.
7. Secretion of the protein when the vesicle fuses
   with the cell membrane during exocytosis.

Question 113

1.4 Describe the
potassium channel.

Answer 113

The potassium channel is an integral membrane
protein that facilitates the diffusion of potassium
ions out of the cell.

Question 114

1.4 Describe the
mechanism of
potassium
movement through
the potassium
channel.

Answer 114

The channel has a “ball and chain” gate
mechanism that will only open the channel for
potassium movement when a specific cell voltage
is reached.

Question 115

Explain the
specificity of the
potassium channel.

Answer 115

Potassium channels are designed to allow the
flow of potassium ions across the membrane, but
to block the flow of other ions–in particular,
sodium ions.

Question 116

1.4 Describe the
action of the
“voltage gate” of
the potassium
channel.

Answer 116

When a neuron is firing, the voltage of the cell
changes. The potassium channel will only open
when the voltage of the cell has reached its peak
(of about 30mv).

Question 117

1.4 Explain what
happens to cells
when placed in
solutions of the
same osmolarity,
higher osmolarity
and lower
osmolarity.

Answer 117

-isotonic solutions are solutions that have the
same osmolarity.
-water moves into and out of the cell equally,
resulting in no NET movement of water.
-hypertonic solutions are solutions that have more
solutes than the cell.
-water will move out of the cell and as a result the
cell will shrivel (animal) or plasmolyze (plant).
-hypotonic solutions are solutions that have fewer
solutes than the cell.
-water will move into the cell. Animal cells will
swell and may burst.
-plant cells will become turgid with a vacuole full
of water and pressure on the cell wall.

Question 118

1.4 Outline the use
of normal saline in
medical
procedures.

Answer 118

-normal saline is a solution of water and salt ions
that is isotonic to human blood.
-it is used as an eye wash, to flush wounds and
intravenously to rehydrate patients
-during organ transplant, while out of a body the
organs are bathed in normal saline.
-because the solution is isotonic to body cells, the
cells will not shrink or swell when exposed to the
saline solution.

Question 119

1.4 Define
osmolarity, isotonic,
hypotonic and
hypertonic.

Answer 119

Osmolarity: the concentration of solutes in a
solution.
Isotonic: the osmolarity of two solutions is the
same.
Hypotonic: a solution with a lower osmolarity
(fewer solutes) compared to another solution.
Hypertonic: a solution with a higher osmolarity
(more solutes) compared to another solution.

Question 120

1.4 State the formula
for calculating the
percentage change
between
measurement
values.

Answer 120

1. calculate the difference between the two
   numbers you are comparing.
2. divide the increase by the original number and
   multiply the answer by 100

Question 121

1.4 Explain how the
standard deviation
is useful for
comparing the
means and the
spread of data
between two or
more samples.

Answer 121

-the smaller the standard deviation, the more
closely the data cluster about the mean.
-this information is useful in comparison to other
datasets using a T-test.

Question 122

1.4 Determine
osmolarity of a
sample given
changes in mass
when placed in
solutions of various
tonicities.

Answer 122

-samples will gain mass when placed in a
hypotonic solution (as water moves into the
sample).
-samples will lose mass when placed in a
hypertonic solution (as water moves out of the
sample).
-there will be zero change in mass when the
sample is placed in an isotonic solution.
-the osmolarity of a sample is the point at which
there is no net movement between the sample
and the solution in which it is placed.

Question 123

1.5 DiscUSS
implications of all
cells being formed
from preexisting
cells.

Answer 123

Implication #l: We can trace the origin of all the
cells in our body back to the first cell; the zygote
produced by the fertilization of a sperm and egg
Implication #2: The origins of all cells can be
traced back through billions of years of evolution
to “LUCA” the last universal common ancestor of
all life on Earth.
Implication #3: There must have been a first cell
that arose from non-living material.

Question 124

1.5 Outline the four
processes needed
for the spontaneous
origin of cells on
Earth.

Answer 124

1. The synthesis of simple organic molecules from
   inorganic compounds.
2. The assembly of these organic molecules into
   polymers.
3. The formation of a polymer that can self
   replicate (enabling inheritance).
4. Packaging of molecules into membranes with
   an internal chemistry different from the
   surroundings.

Question 125

1.5 Outline the
experiments of
Miller and Urey into
the origin of
organic
compounds.

Answer 125

1. boiled water evaporates and moves into the
   larger flask, where it combines with methane,
   ammonia and hydrogen gases in a large flask.
2. sparks are fired between electrodes to simulate
   lightning.
3. a cooling condenser turns steam back into
   liquid water, which drips down into the trap,
   where organic molecules produced in the
   reactions also settle.

Question 126

1.5 Define
polymerization,
monomer and
polymer

Answer 126

Polymerization: The process in which relatively
small molecules, called monomers, combine
chemically to produce a large chainlike molecule,
called a polymer.
Monomer: “one part.” The single building block
unit of a polymer.
Polymer: “many parts.” A large molecule
composed of many monomer subunits

Question 127

1.5 Outline two
properties of RNA
that would have
allowed it to play a
role in the origin of
life

Answer 127

1. RNA can self-replicate.
2. RNA can serve as a genetic code for protein
   synthesis between generations.
3. RNA can act as a catalyst, speeding up the
   polymerization of amino acids to form proteins.

Question 128

1.5 Outline why fatty
acids were likely the
primary component
of the membrane of
early cells.

Answer 128

1. Fatty acids are structurally much simpler than
   phospholipids and may have formed more readily
   in a prebiotic environment.
2. Similar to phospholipids, fatty acids have a
   hydrophobic tail and a hydrophilic head and can
   thus form the same types of structures, such as
   vesicles, micelles and bilayers.

Question 129

1.5 State the
endosymbiosis
theory.

Answer 129

Theory that mitochondria and chloroplasts
evolved from free living prokaryotic cells that
were engulfed (but not digested) by early
eukaryotic cells.
The mitochondria and chloroplasts evolved as
“symbiotic” (together, both benefiting)
“endobionts” (inside living)

Question 130

1.5 Describe the
evidence for the
endosymbiotic
theory.

Answer 130

Mitochondria and chloroplasts share the
following with prokaryotic cells:
- shape
-Size
-70s ribosomes

-circular, naked DNA
-genetic sequences
-movement
-division by binary fission
-inhibited by antibiotics
Additionally, mitochondria and chloroplasts have
a double layer membrane

Question 131

1.5 Define
spontaneous
generation.

Answer 131

The theory, now discredited, that living organisms
can routinely emerge from nonliving matter
independently of other living matter.

Question 132

1.5 Describe
Pasteur’s
experiments about
spontaneous
generation.

Answer 132

Pasteur’s experiments (1859) provided evidence
that spontaneous generation of cells and
organisms does not now occur on Earth.
Pasteur’s experiment consisted of three parts.
1. the broth in the flask was boiled to sterilize it.
When this broth was cooled, it remained free of
microbial contamination.
2. the flask was boiled and then the neck was
broken off. The broth in this flask became cloudy as it became contaminated with microbes from
the air.
3. Pasteur created a flask with a curved neck. The
curve allowed indirect exposure to air but
prevented entry of microbes. The broth remained
free of microbial contamination.

Question 133

1.5 Explain why
Pasteur’s
experiments did not
support the idea of
spontaneous
generation.

Answer 133

-if a life force was responsible for microbial
growth within the sterilized flasks, it would have
access to the broth, whereas the microorganisms
would not.
-however, because the broth in the flask remained
clear, Pasteur’s experiment showed that air does
not contain a “vital force” that creates life. Life
could not spontaneously generate.

Question 134

1.5 Outline historical
thinking about
spontaneous
generation.

Answer 134

Early philosophers and scientists were basing their
ideas on what they could observe at the time.
Technological tools had not yet advanced to the
point of being able to observe cells arising from
other cells.
There was no reason or pressure to show that
spontaneous generation wasn’t accurate. It’s hard
to speak out against an idea when a majority
support it.
Spontaneous generation was consistent with the
other widely held cultural and religious beliefs of
the time.

Question 135

1.4 List four
processes which
involve mitosis.

Answer 135

1. Tissue repair (for example after injury)
2. Growth of the organism
3. Embryonic development
4. Replacement of cells that die naturally (for
   example, skin)
5. Clonal selection of B cells (for antibody
   production)
6. Asexual reproduction (for example budding)

Question 136

1.6 Draw typical
eukaryotic cells as
they would appear
during the
interphase and the
four phases of
mitosis.

Answer 136

Nucleus intact
Nucleolus visible
DNA as chromatin
DNA is unreplicated

Question 137

1.6 Outline four
events that occur
during prophase.

Answer 137

Nuclear membrane breaking down
Nucleolus fading
DNA supercoiling into chromosome
Spindle fibers form
Centrioles more towards cell poles

Question 138

1.6 Outline four
events that occur
during telophase.

Answer 138

Nuclear membrane reforming
Nucleolus reforming
DNA uncoiling to become chromatin
Spindle fibers degrade

Question 139

1.6 Describe the
structure of a
replicated
chromosome,
include the
centromere and
sister chromatids.

Answer 139

Chromosomes are supercoiled strands of DNA
Replicated chromosomes means that there are
identical copies of DNA called sister chromatids
(formed during DNA replication in S phase)
attached to each other at the centromere

Question 140

1.6 Explain why
chromosomes must
condense during
mitosis.

Answer 140

To “condense” means to make DNA denser. or
more tightly packed
DNA condenses during mitosis so that it can more
easily be moved to the poles of the cell without
getting tangled and/or broken.

Question 141

1.6 Define
cytokinesis.

Answer 141

Cytokinesis is the division of the cytoplasm of a
parent cell into two daughter cells.

Question 142

1.6 State the
difference between
mitosis and
cytokinesis.

Answer 142

Mitosis refers to the division of the nucleus
(nuclear DNA) whereas cytokinesis is division of
the cytoplasm (and organelles in it).

Question 143

1.6 Describe the
formation of the
cleavage furrow in
animal cell
cytokinesis.

Answer 143

-microtubule filaments form a concentric ring
around the centre of the cell
-the microfilaments constrict to form a cleavage
furrow, which deepens from the periphery
towards the centre
-plasma membrane at the equator is pulled
inwards until they meet the centre of the cell
-when the furrow meets in the centre, the cell
becomes completely pinched off and two cells
are formed
-because this separation occurs from the outside
and moves towards the centre, it is described as centripetal

Question 144

1.6 Describe the
formation of the
middle cell wall in
plant cell
cytokinesis.

Answer 144

-carbohydrate-rich vesicles form in a row at the
centre of the cell (equatorial plane)
-during telophase, vesicles move to the equator
of the cell.
-vesicles fuse together and an early cell plate
begins to form within the middle of the cell
-cell plate extends outwards and fuses with the
cell wall, dividing the cell into two distinct
daughter cells
-because this separation originates in the centre
and moves laterally, it is described as centrifugal

Question 145

1.6 Define tumor,
benign, malignant,
metastasis, cancer,
mutagen and
carcinogen.

Answer 145

Tumour: A mass of tissue caused by abnormal cell
division.
Benign: (of a disease) not harmful in effect.
Malignant: (of a disease) very virulent or
infectious.
Metastasis: the development of secondary
malignant growths at a distance from a primary
site of cancer.
Cancer: A disease caused by a malignant tumor.
Mutagen: an agent, such as radiation or a
chemical substance, which causes genetic
mutation.
Carcinogen: a substance capable of causing
cancer in living tissue.

Question 146

1.6 Describe why
mutagens are not
necessarily
carcinogens.

Answer 146

A mutagen induces mutations in DNA (any
mutations). If the mutation results in uncontrolled
cell division and cancer, then the mutagen is also
a carcinogen.

Question 147

1.6 Describe how
cancer arises over
time.

Answer 147

-cells become cancerous after mutations
accumulate in genes that control the cell cycle.
-the Cancer Genome Project found that most (not
all) cancer cells possess 60 or more mutations.

Question 148

1.6 Explain the
relationship
between
oncogenes, tumor
suppressor genes
and cancer.

Answer 148

Proto-oncogenes code for proteins that stimulate
the cell cycle and promote cell growth and
proliferation

-when proto-oncogenes mutate (or subjected to
increased expression), they become oncogenes.
-oncogenes move the cell through the cell cycle
even when it shouldn’t divide

Question 149

1.6 Explain why the
existence of a
correlation does
not necessitate a
causal relationship
between two
variables.

Answer 149

For any two correlated variables, the following
relationships are possible:
X causes Y
Y causes X
X and Y are consequences of a common cause,
but do not cause each other

X causes Z which causes Y
The correlation between X and Y is a coincidence

Question 150

1.6 Outline the
discovery of cyclins
including the role of
serendipity.

Answer 150

Tim Hunt was studying embryonic development
when he by chance observed that a protein
would increase and decrease in concentration
with each cycle of cell division.

Question 151

1.1 A Chlorella cell
viewed through a
microscope is
0.00005 m wide
when the
magnification is
*2000. What is the
actual size of the
cell?

Answer 151

0.00005 m ÷ 2 000 = 0.000000025m
Since the answers are given in micrometers, we
must convert.
1 micrometer = le-6 m (0.000001 m) so
0.000000025 m/0.000001 m = 0.025 micrometers

Question 152

1.1 Distinguish
between totipotent,
pluripotent,
multipotent, and
unipotent stem
cells.

Answer 152

Totipotent stem cells
e.g. the eight cells of the morula (the first cells
formed following fertilisation of an egg cell)
-can differentiate into any type of cell including
placental cells.
-can give rise to a complete organism.
Pluripotent stem cells
(e.g. embryonic stem cells of the blastocyst)
-can differentiate into all body cells, but cannot
give rise to a whole organism.
*pluripotent stem cells can only be taken from the
inner cell mass of the blastocyst.
Multipotent stem cells
(e.g. umbilical cord stem cells)
-can differentiate into a few closely related types
of body cell.
Unipotent stem cells
-can only differentiate into their associated cell
type. For example, liver stem cells can only make
liver cells.

Question 153

1.1 List the following
with increasing
sizes:
-bacterium
-plant cell
-virus
-animal cell

Answer 153

virus < bacterium < plant cell = animal cell
100nm < 1um < 100m = 100m

Question 154

1.2 Contrast
structural
differences
between plant cells
and animal cells.

Answer 154

Plant cell:
-cell wall
-chloroplast
-large vacuole
-fixed shape
-starch stored
-no centrioles/no centrosomes
-no lysosome
Animal cell:
-no cell wall
-no chloroplast
-no large vacuole
-no fixed shaped
-glycogen stored
-has centrioles and centrosomes
-contains lysosome

Question 155

1.2 Describe how
the structure of the
membrane allows
the formation of
vesicles.

Answer 155

fluidity of membrane allows change of shape/
invagination/formation of vesicles;
phospholipids can move / phospholipid bilayer
makes membrane fluid/flexible;
weak bonding between phospholipid tails;
bends/kinks in the phospholipid tails prevent
close packing;
cholesterol affects membrane fluidity;

Question 156

1.2 State the
functions of the
following
organelles of a
eukaryotic animal
cell: lysosome,
Golgi apparatus,
free ribosomes.
plasma membrane,
rough endoplasmic
reticulum

Answer 156

lysosome:
a. (from Golgi apparatus) with digestive enzymes /
break down food/organelles/ cell;
Golgi apparatus:
b. site that processes/modifies/packages and
releases proteins;
free ribosomes:
c. site of synthesis of proteins (released to
cytoplasm);
plasma membrane:
d. controls entry and exit of materials/substances
in cell;
rough endoplasmic reticulum:
e. synthesis and transport of proteins; (both
needed)

Question 157

1.2 Compare
prokaryotic and
eukaryotic cells.

Answer 157

Prokaryote:
-naked DNA
-DNA in cytoplasm/no nucleus
-70S ribosomes
-no membrane-bound organelles
-circular chromosome
-fission
-no introns or exons
-smaller in size (approximate) 10 microns
-cell wall present
Eukaryote:
-DNA associated with proteins
-DNA enclosed in a nuclear envelope
-80S ribosomes
-internal membranes that form membrane bound
organelles
-linear chromosomes
-mitosis
-have introns and exons
-larger in size up to (approximately) 100 microns
-cell wall only present in plants/fungi

Question 158

1.2 State the role of
centrioles.

Answer 158

Centrioles are responsible for the production of
microtubules and spindle fires that are essential
for cell division.

Question 159

1.1 Define
micrograph.

Answer 159

A photograph taken by means of a microscope

Question 160

1.4 Define
pinocytosis.

Answer 160

Taking in of liquid substances by living cells

Question 161

1.4 Compare and
contrast pinocytosis
and phagocytosis.

Answer 161

In summary, pinocytosis and phagocytosis are two types of endocytosis that involve the uptake of materials from the environment. Pinocytosis is a non-specific process that involves the uptake of fluids and small molecules, while phagocytosis is a selective process that involves the uptake of larger solid particles such as microorganisms and dead cells.

Question 162

1.4 Define isotonic
osmolarity.

Answer 162

When the concentration of water is the same on
both sides of a membrane there is no net
movement.

Question 163

1.5 List the
necessary
conditions for life to
come into being
and then to persist

Answer 163

Simple organic molecules, such as amino acids,
fatty acids and small carbohydrates, must be
formed.
Larger organic molecules, such as phospholipids,
RNA and DNA, must be assembled from simpler
molecules.

Biochemical reactions require set conditions, such
as pH. Therefore, self-contained structures such
as membranes, are necessary

Question 164

1.5 Describe the
early atmospheric
conditions.

Answer 164

Low oxygen atmosphere with high radiation
levels, high temperatures and electrical storms.

Question 165

1.5 State the name
of the French
microbiologist who
was responsible for
proving that cells
came from pre.
existing cells.

Answer 165

Louis Pasteur

Question 166

1.5 Biologists
suspect that
endosymbiosis gave
rise to mitochondria
before chloroplasts
because:

Answer 166

All eukaryotes have mitochondria, whereas many
eukaryotes do not have chloroplasts.

Question 167

1.5 State the
evidence that
supports that
prokaryotes
evolved before
eukaryotes

Answer 167

The oldest fossilised cells resemble prokaryotes.

Question 168

1.5 A cell that is
dividing too rapidly
may have lost its
ability to enter
which part of the
cell cycle?

Answer 168

Gl
Without entering Gl, a cell may divide too rapidly
and this leads to uncontrolled growth and
formation of a tumour. “Interphase” cannot be the
correct answer because S phase is part of
interphase. The cell cannot divide if it has not
duplicated its DNA.

Question 169

1.5 State the name
of the cyclin that
increases to trigger
the beginning of
mitosis

Answer 169

When cyclin B reaches its peak mitosis can begin.

Question 170

1.6 State the name
of the molecule that
CDKs attach to
proteins in order to
activate them.

Answer 170

phosphate group

Question 171

1.6 DNA is loosely
packaged by
histones to form
which molecule?

Answer 171

chromatin/nucleosome
Chromatin is the name of the combination of DNA
with proteins. The smallest unit of the association
of DNA with histones is the nucleosome. (Note
that there is no plural of “chromatin”, so
“chromatins” is incorrect).

Question 172

1.6 Define
chromatin.

Answer 172

a substance within a chromosome consisting of
DNA and protein.

Question 173

1.3 Outline how
temperature affects
cell membrane
fluidity.

Answer 173

As temperature increases, so does phospholipid
bilayer fluidity. At lower temperatures,
phospholipids in the bilayer do not have as much
kinetic energy and they cluster together more
closely, increasing intermolecular interactions and
decreasing membrane fluidity.

Question 174

1.6 State the role of
cyclins D, B, A and E
in the cell cycle.

Answer 174

Cyclin D: Cyclin D is important for the G1 phase of the cell cycle, where it binds to and activates CDK4 and CDK6. The Cyclin D-CDK4/6 complex promotes the phosphorylation of the retinoblastoma protein (Rb), releasing E2F transcription factors and allowing cells to enter the S phase of the cell cycle.
Cyclin E: Cyclin E is also important for the G1 phase of the cell cycle, where it binds to and activates CDK2. The Cyclin E-CDK2 complex promotes DNA replication and the initiation of the S phase.
Cyclin A: Cyclin A is important for the S phase of the cell cycle and is expressed during the G2 phase as well. Cyclin A binds to and activates CDK2, promoting the completion of DNA replication and the initiation of mitosis.
Cyclin B: Cyclin B is important for the G2/M phase transition, where it binds to and activates CDK1. The Cyclin B-CDK1 complex drives cells into mitosis by promoting the assembly of the mitotic spindle and the segregation of chromosomes

Question 175

1.2 List six examples
of exocrine gland
cells.

Answer 175

Sweat glands secrete water as a coolant (2.2.A2)
Salivary glands secrete mucus and amylase during
digestion (6.1.S1)
Mammary glands secrete milk (D.5.A2)
Gastric glands secrete HCI, mucus and digestive
enzymes in the stomach (D.2.U3)

Mucous glands secrete mucus for lubrication and
immune defense (6.3.U1)
Sebaceous glands secrete a waxy oil that
lubricates and waterproofs the skin and hair/fur
(6.3.U1)