1 - cell biology

Question 1

functions of:
1. ribosome
2. soft endoplasmic reticulum
3. rough endoplasmic reticulum
4. golgi apparatus
5. lysosome

Answer 1

1. intracellular protein synthesis
2. lipid synthesis
3. extracellular protein synthesis
4. modify and package proteins so they become vesicles
5. break down worn out organelles using digestive enzymes

Question 2

outline processes during interphase in the cell cycle [3]

Answer 2

increase in cell size
number of organelles are doubled
DNA replication
mRNA production
protein synthesis
cell respiration

Question 3

what are and what is the role of cyclins in the cell cycle? [2]

Answer 3

group of regulatory proteins that regulate the cell cycle
activate cell-dependent kinases (CDK enzyme) that control cell cycle processes

Question 4

outline the therapeutic use of stem cells [3]

Answer 4

stem cells are unspecialized cells capable of self-renewal and differentiation
accessible in the bone marrow / embryo / umbilical cord blood
due to self-renewal, they can repair damaged tissues
example 1: Stargardt’s disease, where stem cells are injected under the retina
example 2: leukemia

Question 5

what are stem cells?

Answer 5

undifferentiated cells that can undergo self-renewal and have the capacity to differentiate into specialised cells

Question 6

outline the significance of surface area to volume ratio in the limitation of cell size. [4]

Answer 6

• S.A. of the cell affects the rate of material exchange
• when cell increases size, so does its volume and metabolism —> more substances needed to be taken in
• S.A. to volume ratio gets smaller
• substances cannot enter the cell efficiently as diffusion rate decreases
• so ratio limits cell size

Question 7

describe transport across cell membranes by osmosis [4]

Answer 7

osmosis is a form of diffusion
movement of water molecules across a partially permeable membrane
from region of high to low Ψ
aquaporins are used

Question 8

list 4 structures seen under the electron microscope in human gametes that are not present in prokaryotic cells [4]

Answer 8

nucleus
membrane bound organelles
mitrochondria
rough ER/smooth ER/golgi apparatus
lysosomes/centrosomes
ribosomes
chromosomes/histones

Question 9

outline the cell theory. [2]

Answer 9

cells can only come from pre-existing cells
cells are the smallest unit of life
there are atypical cells

Question 10

discuss the cell theory and its limitations. [7]

Answer 10

cell theory:
cell theory is the accepted explanation of life
organisms are composed of one or more cells
cells are the smallest unit of life
cells can only come from pre-existing cells

limitations (atypical cells):
striated muscle cells are multi-nucleated
giant algae have complex single cell structure
aseptate fungal hyphae have no cell membranes between nuclei
viruses have characteristics of living organisms but are not cells

Question 11

describe the processes involved in absorbing different nutrients across the cell membrane of villus epithelium cells lining the small intestine

Answer 11

diffusion: of nutrients like transporting fatty acids
facilitated diffusion: involving channel proteins like transporting fructose
active transport: against concentration gradient using protein pumps like transporting ions
endocytosis using vesicles

Question 12

describe the origin of eukaryotic cells according to the endosymbiotic theory [4]

Answer 12

chloroplasts and mitochondria were once free living organisms 😌
a big bad cell took in another cell by endocytosis 👹 but did not digest the cell

evidence:
double membrane (around chloroplast mitochondrion)
division/binary fission
70s ribosomes

Question 13

outline the cell cycle [4]

Answer 13

mitosis is the division of cell resulting in two genetically identical daughter cells
consist of prophase, metaphase, anaphase and telophase
cytokinesis happens after mitosis
interphase happens before mitosis, consisting of G1, S and G2 phases where DNA is replicated

Question 14

describe how pasteur’s experiments provided evidence to falsify spontaneous generation. [3]

Answer 14

spontaneous generation refers to life appearing from non-living cells
culture medium put in flasks, is boiled to kill microbes
after necks of glass broken, culture turned cloudy
suggesting microbes in air contaminated the culture

(dead swans attract microbes)

Question 15

explain how the cell cycle is controlled [4]

Answer 15

cell cycle is G1, S, G2 and mitosis
cell cycle controlled by four cyclins
levels of cyclins will fluctuate at different stages
cyclins bind to the cyclin-dependent kinases to activate them

Question 16

2 advantages of electron over light microscopes

Answer 16

much higher range of magnification
much higher resolution

Question 17

describe processes during mitosis [8]
(two for each in PMAT)

Answer 17

prophase: nuclear membrane breaks down, chromosomes condense by supercoiling
metaphase: spindle fibers attach to centromere of chromosomes, chromosomes align along equator
anaphase: spindle fibers contract, sister chromatids pulled opp. poles
telophase: nuclear membrane reforms, chromosomes decondense

Question 18

describe four different types of transport of substances across membrane [4]

Answer 18

• simple diffusion
• facilitated diffusion (through channel proteins)
• osmosis (through PPM)
• active transport (against gradient using ATP)
• exocytosis (vesicle attach to membrane to release)
• endocytosis (vesicle attach to membrane to bring in)

Question 19

describe endocytosis [5]

Answer 19

• fluidity of membrane allows endocytosis
• plasma membrane forms pit to receive substance transported
• vesicle forms around substance
• inside of plasma membrane becomes outside of vesicle
• process is active and requires energy

Question 20

discuss alternative models of membrane structure including evidence for or against each model [8]

Answer 20

• early models showed membranes are partially permeable
• evidence for: chemical analysis showed membrane consist of proteins and lipid
• Davson-Danielli model proposed phospholipid bilayer with protein on both surfaces
• sandwich structure (two dark bands one light band)
• evidence for: electron microscopy
• evidence against: falsified by freeze fracturing, low resolution of electron micrograph
• led to fluid-mosaic model of proteins floating inside the bilayer
• suggest presence of integral and peripheral proteins

Question 21

how hydrophilic and hydrophobic properties contribute to arrange of molecules in membrane [7]

Answer 21

• hydrophilic means attracted to water
• hydrophobic means not attracted to water
• membrane is phospholipid bilayer
• containing hydrophilic phosphate head and hydrophobic phosphate tail
• tails face inwards, heads face outwards
• phospholipids are thus amphipathic, granting membrane fluidity to facilitate vesicle formation
• peripheral proteins are hydrophilic, so can locate on surface of membrane
• exterior of channel proteins are hydrophobic, so they are embedded
• interior of channel proteins are hydrophilic, so ease entry/exit of substances