cell transport

Question 1

Describe the structure of a cell membrane. (5)

Answer 1

Double layer of phospholipid molecules;
Detail of arrangement of phospholipids;
Intrinsic proteins passing right through;
Some with channels
Extrinsic proteins only on surface;
Molecules can move in membrane;
membrane contains cholesterol;
carbohydrates attached to proteins;

Question 2

Describe two ways in which the appearance of a plant cell wall would differ from a
cell membrane when viewed with an electron microscope. (2)

Answer 2

Thicker;

Single layer of fibrils in cell wal

Question 3

Describe the part played by cell surface membranes in regulating the movement of
substances into and out of cells. (6)

Answer 3

lipid soluble molecules AND small molecules can move through phospholipid bilayer though diffusion;
water soluble and large molecules move through protein channels
Carrier proteins move substances against a concentration gradient;
through active transport which requires ATP;
Different cells have different proteins;

Question 4

Describe how the distribution of cell membranes in a prokaryotic cell such as a bacterium
differs from that in a cell from a plant leaf. (4)

Answer 4

in prokaryotes:
No nuclear envelope;
No Membrane bounded organelles;
Such as mitochondria or chloroplast;
Mesosomes in prokaryotes instead of mitochondria;
No membrane systems such as Golgi body;

Question 5

describe the property of the cell surface membrane which allows osmosis to take
place. (1)

Answer 5

Partially permeable

Question 6

Describe two ways in which
you would expect the movement of water into a cell by osmosis to be similar to the
diffusion of oxygen into a cell. (2)

Answer 6

Passive;

movement down gradient;

Question 7

State Fick’s Law.

Answer 7

(SA x diff in conc)/ difusion pathw

Question 8

Explain how amino acid molecules may be linked to form a polypeptide chain which is
folded into a specific tertiary shape. (6)

Answer 8

Condensation;
removal of water molecule;
from amino and carboxyl groups;
forming peptide bonds;
if same amino acids are in the same sequence;
bonds formed between R-groups;
e.g. hydrogen bonds;
form in the same place;
resulting in a specific tertiary shape

Question 9

Describe the role of proteins in the transport of molecules and ions across cell surface
membranes. (7)

Answer 9

Allows passage of charged ions across membrane;
allows passage of water soluble and large molecules;
both though channel proteins

carrier proteins;
specificity lined to shape of receptor sites;
functions by changing shape / conformation;

facilitated diffusion with concentration gradient;
active transport against concentration gradient;
active transport requiring energy / ATP;

Question 10

The hormone glucagon is a protein. It targets liver cells but does not affect other cells in
the body. Explain why. (4)

Answer 10

Glucagon has specific shape;
receptor molecules with specific receptor sites;
glucagon has a complementory shape to liver cells;
glucagon receptors only on liver cells;

Question 11

Give two ways in which active transport differs from diffusion.

Answer 11

ATP used;

movement is against a concentration gradient;

Question 12

Explain how the addition of cyanide ions would affect the uptake of sodium ions by a cell.

Answer 12

less movement of ions;
movement of ions needs ATP;
respiration produces ATP

Question 13

Explain why facilitated diffusion’s rate of uptake platoue at high concentration difference

Answer 13

At high concentrations the rate is limited by

the number of transport proteins.

Question 14

Explain why facilitated diffusion through membrane’s rate of uptake are similar up to a certain point?

Answer 14

both have greater concentration difference

Question 15

Where, in the cell, do enzymes control glycolysis?

Answer 15

cytoplasm

Question 16

Explain why a mitochondria that is in a cell with a higher metabolic rate have more cristea

Answer 16

Cristae are site of ATP synthesis:
by electron carriers;
Metabolism requires ATP;

Question 17

Cholera bacteria produce toxins which increase secretion of chloride ions into the
lumen of the intestine.
Explain why this results in severe diarrhoea

Answer 17

1. water leaves cells;
2. due to lower water potential in the lumen of intestine ;
3. by osmosis down a WP gradient;
4. not enough water reabsorbed in the intestines;

Question 18

What are the 6 functions of proteins in the cell membrane

Answer 18

1. Provide structural support
2. Act as channels to transport water-soluble substances
3. Allow active transport via carrier protein
4. Form cell-surface receptors for identifying cells (antigens)
5. Help cells adhere together (form tissues)
6. Act as receptors e.g. For hormones

Question 19

Give the 3 functions cholesterol

Answer 19

1. Reduce lateral movement of other molecules
2. Make the membrane less fluid at high temperatures
3. Prevent leakage of water and dissolved ions from the cells

Question 20

Give 3 functions of glycolipids

Answer 20

1. Act as recognition sites
2. Help maintain the stability of the membrane
3. Help cells to attach one another’s a so form tissues

Question 21

Give 3 functions of glycoproteins

Answer 21

1. Act as recognition sites
2. Help cells to attach to one another to form tissues
3. Allows cells to recognise one another

Question 22

What are the three functions of nucleus

Answer 22

1. Act as a control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
2. Retain the genetic material of the cell in the form of DNA and chromosomes
3. Manufacturer ribosomal RNA and ribosomes

Question 23

What does matrix of mitochondria contain? Name 4

Answer 23

Protein
Lipids
Ribosomes
DNA

Question 24

How are chloroplasts adapted for their function? Give 3 examples

Answer 24

1. Large surface area for the attachment of chlorophyll, enzymes and electron carriers
2. The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis
3. chloroplast contain both DNA and ribosomes so they can quickly and easily manufacturer some of the proteins needed for photosynthesis

Question 25

Give two functions of RER

Answer 25

1. Provide large SA for the synthesis of proteins and glycoproteins
2. Provide a pathway for the transport of materials (proteins) throughout the cell

Question 26

Give two functions of SER

Answer 26

1. Synthesis, store and transport lipids

2. Synthesis, store and transport carbohydrates

Question 27

Give 5 limitations of TEM micriscope

Answer 27

1. complex staining
2. artifacts present
3. cannot look at living organisms
4. specimen must be very thin
5. image only in 2D

Question 28

describe 4 principles of TEM microscopes

Answer 28

1. Electrons pass through thin specimen;
2. Denser parts absorb more electrons;
3. So denser parts appear darker;
4. Electrons have short wavelength so give high resolution;

Question 29

Give the 5 functions of the Golgi body

Answer 29

1. add carbohydrates to proteins to form glycoproteins
2. produce secretory enzymes, such as those secreted by the pancreas
3. secrete carbohydrates, such as hose used in making cell walls in plants
4. transport, modify and store lipids
5. form lysosomes

Question 30

When and how are lysosomes formed in the golgi body?

Answer 30

lysosomes are formed when the vesicles produced by golgi body contain enzymes such as proteases and lipases. they also contain lysozymes.

Question 31

Give the 4 functions of lysosomes

Answer 31

1. hydrolyse material ingested by phagocytic cells
2. release enzymes to the outside of the cell (exocytosis) in order to destroy materials around the cell
3. digest worn out organelles so that the useful chemicals they are made of can be re-used
4. completely break down cells after they have died (autolysis)

Question 32

Given the functions of lysosomes, what type of cells are they abundant in? and give two examples

Answer 32

secretory cells such as

1. epithelial
2. phagocytic

Question 33

What are the two features of cell walls?

Answer 33

1. they consist of a number of polysaccharides such as cellulose
2. there is a thin layer called the middle lamella which marks the boundary between adjacent cell walls and cements adjacent cells together

Question 34

Give the 3 features of cellulose in cell walls

Answer 34

1. to provide mechanical strength in order o prevent the cell bursting under the pressure created by osmotic entry of water
2. to give mechanical strength o the plant as a whole
3. to allow water to pass along it and so contribute to the movement of water through the plant

Question 35

What is the single membrane around a vacuole called?

Answer 35

the tonoplast

Question 36

What are the 3 functions of plant vacuoles?

Answer 36

1. they support herbaceous plants by making cells turgid
2. the sugars and amino acids may act as a temporary food store
3. the pigments may colour petals to attract pollinating insects

Question 37

Give 2 examples of tissues

Answer 37

xylem tissue

epithelial tissue