Ultrastructure QP q's

Question 1

Describe the structure of a plasma (cell surface) membrane.

Answer 1

Phospholipid bilayer containing proteins, where the hydrophilic phosphate heads face outwards and the fatty acid tails which are hydrophobic face inwards.Intrinsic glycoproteins span the entire membrane. Extrinsic glycoproteins are on the periphery of the membrane. Glycoproteins and glycolipids stick out of the bilayer/ membrane. Cholesterol is inside the bilayer.

Question 2

Suggest the mechanism by which the indicator enters the cells and suggest the
component of the membrane involved.

Answer 2

active transport
carrier protein

Question 3

The student took a small sample from suspension A and added alkaline ammonia
solution. There was no colour change.
What could the student conclude about the permeability of the yeast plasma membrane?

Answer 3

not permeable to ammonia

Question 4

The student suggested that the liquid in the suspension was yellow because boiling the
yeast had damaged the plasma membrane, allowing the indicator out of the cells.
Describe the effect of high temperature on the structure of the yeast cell membranes.

Answer 4

the phospholipids have more kinetic energy and so vibrate more. This increses the size/no. gaps between the phospholipids in the membrane. The bilayer melts and becomes more fluid. This denatures the glycoproteins.

Question 5

cells. (a) State two functions of membranes within cells.

Answer 5

separates contents of organelles from cytoplasm

provides surface for attachment of enzymes

Question 6

Describe the arrangement and functions of two named components of a cell surface
membrane.

Answer 6

hydrophobic phospholipid tails point inwards and phospholipid hydrophilic heads point outwards to form the bilayer, acting as barrier to large polar molecules

Cholesterol molecules fit within the bilayer to stabilise membrane structure and regulate fluidity

Question 6

arrangement and function of proteins?

Answer 6

form channels/carriers for active transport/facilitated diffusion

Question 7

arrangement and function of glycoproteins/glycolipids?

Answer 7

on the surface of the cell surface membrane for cell signalling/stabilising cell shape

Question 8

Which component of a cell membrane becomes more fluid as temperature increases?

Answer 8

phospholipid bilayer

Question 9

Which component of a cell membrane denatures as temperature increases?

Answer 9

glycoproteins

Question 10

Liver cells contain membrane-bound organelles called peroxisomes. These organelles
contain catalase, an enzyme that breaks down hydrogen peroxide to release oxygen
gas.
The student observed that the cube of liver that had been frozen and defrosted, bubbled
significantly more than the cube that had been refrigerated.
Suggest an explanation for this result.

Answer 10

freezing the liver cell causes damage to the peroxisome, so more permeability in the cell membrane to hydrogen peroxide, so my hydrogen peroxide is broken down, releasing more oxygen

Question 11

State the term used to describe a membrane through which some substances can pass freely
but others cannot.

Answer 11

partially permeable

Question 12

State what is meant by cell signalling.

Answer 12

communication between cells. A molecule released by one cell attaches to/causes a change in another cell

Question 13

Explain how cell surface membranes contribute to the process of cell signalling.

Answer 13

release of signal molecule by exocytosis. Glycoproteins/glycolipids act as specific receptors. The shape of the receptor and signal molecule are complementary. Attachment of the signal molecule causes a change on the cell surface. The cell surface membrane then allows for the entry of some signal molecules

Question 14

State three roles of membranes inside cells.

Answer 14

They form compartments for organelles within a cell such as lysosomes, mitochondria etc.
Provides selective permeability.
Site for attachment of enzymes

Question 15

Outline how the vesicles are moved from one organelle to another.

Answer 15

cytoskeleton provide pathways for movement
vesicles move along microtubules. ATP is used to drive this movement

Question 16

• Vesicles that transport materials from the Golgi to the rough endoplasmic
  reticulum (RER) are coated in COPI proteins.
• Vesicles that transport materials to the Golgi from the RER are coated in COPII
  proteins.
  Suggest how these proteins ensure that a vesicle is transported to the correct target
  organelle.

Answer 16

There is a receptor found on the target organelle.
The address protein provides a way of recognising the vesicle. the COPII/COPI has a specific shape, so the shape of the receptor on the target organelle and the address protein are complementary.

Question 17

Cells in the pancreas secrete proteins such as the enzymes pancreatic amylase and protease.
Describe how these extracellular enzymes are secreted from the cells.

Answer 17

by exocytosis as the vesicle fuses with the plasma membrane, which releases the enzyme to the exterior.

Question 18

List three components of a cell surface membrane.

Answer 18

phospholipids
cholesterol
glycoproteins

Question 19

Explain what is meant by the term active transport.

Answer 19

movement of substances against a concentration gradient, using ATP, with the use of a carrier protein

Question 20

State two examples of active transport in cells.
For each example, you should name the substance that is transported and the cell
involved.

Answer 20

mineral ions into root hair cells
hydrogen ions into companion cells

Question 21

facilitated diffusion

Answer 21

passive transport of molecules across a membrane, with the help of transmembrane proteins

Question 22

Describe the routes that water molecules take through the cell surface membrane.

Answer 22

the fit between the phospholipids, go through the phospholipid bilayer, via protein channels

Question 23

Explain why plant cells do not burst when they are left in pure water.

Answer 23

the cell wall provides strength which prevents the cell from over-expanding which limits the cell’s uptake of water`

Question 24

Suggest how the student could construct and use a graph to obtain a better estimate of
the water potential.

Answer 24

plot percentage plasmolysed against the water potential
then read down from 50 percent plasmolysed to the water potential.

Question 25

Yeast cells take up methylene blue by active transport.
Using only the information provided in Table 3.1, outline the evidence that supports this
statement.

Answer 25

at high temperatures the cell denatured, so no ATP for active transport.

Question 26

Suggest why some cells did not stain blue at 20 °C.

Answer 26

some cells may have been dead or not respiring, so no ATP to take up the blue stain

Question 27

Suggest one change that occurred to the plasma (cell surface) membranes of the yeast
cells at temperatures above 60 °C where blue stain started to leak out.

Answer 27

membrane structure disrupted. The phospholipid bilayer then melts, so the membrane proteins also denature and are unable to function, making the membrane more permeable

Question 28

Explain why the stained yeast cells lost their colour at higher temperatures.

Answer 28

the membraine became permeable to stain, so the mthyl blue leaked out of the cells by diffusion

Question 29

The student concluded that yeast cells are killed between 50 °C and 70 °C.
Suggest one way in which the student could have improved the accuracy of this experiment
and one way in which he could have improved the reliability.

Answer 29

to improve accuracy take readings at intermediate temperatures between 50 and 70 degrees

to improve reliability take more readings at each temperature

Question 30

Outline the process of budding in yeast.

Answer 30

the nucleus divides by mitosis as the cell swells on one side, causing the organelles to move into a bud, which then pinches off and the cell wall forms, so the bud becomes a separate cell

Question 31

Membranes contain a variety of proteins. Some of these proteins are combined with
carbohydrates to form glycoproteins.
Describe the functions of glycoproteins in the cell surface membrane.

Answer 31

They act as antigens. They’re involved in the identification of cells as self/non-self. Used for cell signalling. Used as the binding site for hormones/drugs and transport proteins. They hold cells together in a tissue. They attach to water molecules to stabilise the membrane

Question 32

Function for cholesterol

Answer 32

to stabilise the membrane OR maintain fluidity

Question 33

function for protein in the bilayer

Answer 33

allow communication across the membrane OR allow particles to pass through

Question 34

function of phospholipid bilayer

Answer 34

to act as a barrier to charged particles

Question 35

Explain how a glycoprotein can act as a receptor.

Answer 35

the specific shape of the receptor is complementary to the shape of the trigger molecule. So the trigger then binds to the receptor

Question 36

Explain what is meant by the term cell signalling.

Answer 36

it is the communication between cells. So after cell recognition, the cells work together to trigger a response inside the cell

Question 37

The results show that below 50 °C little pigment had entered the water.
Explain why there was no transmission of light after the beetroot had been placed in
water at 100 °C.

Answer 37

The cell surface membrane got damaged, so then the pigment leaked out, and this pigment then absorbed all of the light, so there was zero light transmission

Question 38

A student investigated the effect of temperature on the release of pigment from pieces of
beetroot.
Suggest three ways in which the student could have improved her investigation.

Answer 38

use the same part of beetroot
use more samples at each temperature
rinse/blot the beetroot after cutting

Question 39

a plant cell that has been placed in a concentrated sugar solution M [3]
(b) Explain, using the term water potential, what has happened to cell M.

Answer 39

the water moves out of the cell by osmosis as the cell has a higher water potential than its surroundings, so the water moves down a water potential gradient from a higher water potential to a lower water potential

Question 40

Outline the ways in which substances, other than water, can enter a cell through the plasma
(cell surface) membrane.

Answer 40

small non-polar substances travel through the membrane by diffusion

large substances travel through the membrane using carrier proteins (requiring ATP), by endocytosis

polar substances travel through the membrane by channel proteins, using transport proteins

Question 41

Name the type of nuclear division that occurs in plant growth.

Answer 41

mitosis

Question 42

Explain why the new branches in Fig. 3.2 are seen growing from a position just under the bark
of the cut surface.

Answer 42

because this is where the cambium is found. Mitosis occurs in the cambium to create new cells for growth. These cells differentiate/specialize. The xylem provides water for cell growth and the phloem provides sugars for energy

Question 43

Name one other location where growth occurs in a plant.

Answer 43

the tip, the meristem, the bud

Question 44

These are areas of loosely packed cells in the bark
called lenticels. Lenticels allow gases to diffuse into the living tissues of the trunk.
Suggest why lenticels are essential to the survival of large multicellular plants and explain
why similar structures are not found in large multicellular animals.

Answer 44

it allows oxygen to reach the cells under the bark for aerobic respiration. In animals, they transport oxygen in the blood/ their transport system, however plants do not transport much oxygen in their transport system as oxygen supply from the leaves is limited, considering that stomata only open up in the day, and during winter there are no leaves

Question 45

function of SER

Answer 45

synthesis of fats/ lipids/steroid hormones/ carbohydrates

Question 46

function of lysosome

Answer 46

contain hydrolizing enzymes to break down cells

Question 47

function of ribosomes

Answer 47

protein synthesis

Question 48

The cytoskeleton in cells consists of microtubules and microfilaments.
Describe the roles of the cytoskeleton.

Answer 48

supports the whole cell.
aids to the movement of cilia.
helps with the cell changing shape.
aids to the movement of vesicles.
aids to the movement of chromosomes.

Question 49

The pancreas is an organ that secretes protease enzymes.
Outline how the organelles in pancreatic cells work together to produce and release these
protein molecules from the cells.

Answer 49

the nucleus contains the gene for protein
the RER is the site of protein synthesis
the vesicles transport the protein
the golgi apparatus modifies the proteins
the vesicle fuses to the plasma membrane

Question 50

function of mitochondria

Answer 50

site of aerobic respiration

Question 51

function of SER

Answer 51

transports fats/lipids/steroids/carbohydrates

Question 52

A student suggested that the details of component C could be seen clearly with a very good
light microscope.
Explain why the student is not correct.

Answer 52

because the size of the mitochondria is too small and the resolution of the light microscope is not high enough

Question 53

Describe the advantages of staining specimens to be viewed under a microscope.

Answer 53

you can see more detail
staining provides more contrast

Question 54

Suggest one type of extracellular protein secreted at

Answer 54

enzyme/peptide hormone/glycoprotein

Question 55

Suggest one stage during the secretion of a protein that requires energy.

Answer 55

transport vesicles to plasma cell membrane, leading to the fusion of the vesicle to the membrane - exocytosis

Question 56

Outline the role of the Golgi apparatus.

Answer 56

receives proteins from the RER.
modifies the proteins.
Re-packages them into vesicles.
makes lysosomes.
replenishes the plasma surface membrane.
Synthesises lipids.

Question 57

Name one feature that would be present in the cytoplasm of a prokaryotic cell that is not
found in a eukaryotic cell.

Answer 57

free, circular DNA.
Plasmid.
70s Ribosomes

Question 58

A student wanted to observe some red blood cells under the microscope. The student placed
a small sample of blood onto a microscope slide and added a drop of distilled water. When
viewed at high power, the student observed that the red blood cells had burst.
In a similar procedure using plant epidermis, the student observed that the plant cells did not
burst.
(i) Explain these observations.

Answer 58

the cytoplasm has a lower water potential than the distilled water. This causes the water to move into the cell down the water potential gradient. The water moves into the cell by osmosis. The plasma membrane of the red blood cells becomes weaker and bursts as it cannot withstand the pressure. However, the cell wall of the plant cell is stronger so does not burst as it can withstand the pressure. The plant cell then becomes turgid, so reduces the water uptake.

Question 59

Suggest how the student could modify the procedure to observe red blood cells without
them bursting.

Answer 59

they could use a salt/sugar solution.
They could use a solution with the same water potential as the blood cells.

Question 60

Name the mechanism by which oxygen enters the red blood cells.

Answer 60

diffusion

Question 61

State the process by which root epidermal cells absorb minerals from the soil and describe
how these cells are specialised to achieve absorption.

Answer 61

The cells have extensions/hair.
Large surface area.
Many carrier proteins in the cell surface membrane.
Thin cell walls. More mitochondria

Question 62

Describe how the DNA molecule replicates.

Answer 62

semi conservative replication. Where the double helix untwists, and the hydrogen bonds break between bases for the formation of a new molecule. Free nucleotides align with an exposed bases for complementary base pairing, then the hydrogen bonds re-form. The sugar phosphate backbone forms. DNA polymerase joins the backbone. Each new DNA molecule has one new and one old strand.

Question 63

State, using only the information in Fig. 4.1, one other way to distinguish between DNA
and mRNA.

Answer 63

mRNA is single-stranded
mRNA is non-helical

Question 64

Give one further difference in structure between DNA and RNA.

Answer 64

rNA contains ribose and DNA contains deoxyribose.
rNA contains uracil whereas DNA contains thyomine

Question 65

A gene

Answer 65

A sequence of DNA nucleotides that codes for a protein

Question 66

Suggest why DNA is not able to leave the nucleus.

Answer 66

It is too big to fit through the pore in the nuclear envelope

Question 67

Explain why the mRNA molecule is shorter than a DNA molecule.

Answer 67

It only copies one gene of DNA, whereas DNA copies many genes

Question 68

Explain how α-amanitin stops the formation of an enzyme-substrate complex during RNA
production.

Answer 68

It is a non-competitive inhibitor, where it fits into an allosteric site (place other than the active site), causing the active site to change shape, so the substrate is no longer complementary to the active site.

Question 69

Suggest how the toxin α-amanitin may lead to the death of an organism.

Answer 69

it inhibits the production of mRNA, so no more protein synthsesis, therefore processes such as respiration and/or photosynthesis cannot take place, leading to eventual death of an organism

Question 70

When proteins are heated to a high temperature, their tertiary structure is disrupted.
Explain how this occurs.

Answer 70

increased kinetic energy
polypeptide chains vibrate
hydrogen interactions break
change in 3D shape of the protein, then it denatures

Question 72

The student suggested that the liquid in the suspension was yellow because boiling the
yeast had damaged the plasma membrane, allowing the indicator out of the cells.
Describe the effect of high temperature on the structure of the yeast cell membranes.

Answer 72

the phospholipids have more kinetic energy and so vibrate more. This increses the size/no. gaps between the phospholipids in the membrane. The bilayer melts and becomes more fluid. This denatures the glycoproteins.