Cells

Question 1

4 marks

Describe the structure and function of the nucleus.

Answer 1

Structure
1. Nuclear envelope and pores/ Double membrane and pores
2. Chromosomes/ DNA with histones
3. Nucleolus
Function
4. Holds genetic material for polypeptides production
5. DNA replication occurs
6. Production of mRNA/tRNA
7. Production of rRNA/ribosomes

Question 2

What does it mean if cells become flaccid or turgid

Answer 2

• If cells become turgid cells show water is absorbed by osmosis
• If cells become turgid cells show cells have a lower water potential
• If cells are not flaccid/plasmolysis cells show water is not lost by osmosis

Question 3

2 marks

Give two features of all prokaryotic cells that are not features of eukaryotic cells

Answer 3

• No membrane-bound organelles
• Circular DNA
• Murein in cell wall

Question 4

1 mark

Name the main polymer that forms the following cell walls.
Plant cell wall
Fungal cell wall

Answer 4

Cellulose (plants) and Chitin (fungi)

Question 5

6 marks

Contrast how an optical microscope and a transmission electron microscope work
and contrast the limitations of their use when studying cells.

Answer 5

1. TEM uses electrons and optical uses light
2. TEM allows a greater resolution
3. So with TEM smaller organelles can be observed e.g. ribosome
4. TEM view only dead specimens and optical can view live specimens
5. TEM requires thinner specimens
6. TEM requires a more complex/ time consuming preperation
7. TEM focuses using magnets and optical uses glass lenses

Question 6

5 marks

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.

Answer 6

Comparisons
1. Nucleotide structure is identical
2. Nucleotides joined by phosphodiester bond
3. DNA in mitochondria and chloroplasts same structure to DNA in prokaryotes
Compare
4. Eukaryotic DNA is longer
5. Eukaryotic DNA contain introns, prokaryotic DNA does not
6. Eukaryotic DNA is linear, prokaryotic DNA is circular
7. Eukaryotic DNA is associated with histones proteins, prokaryotic DNA is not

Question 7

Define pathogen

Answer 7

Microorganism that causes disease/ an immune response

Question 8

5 marks

Describe difference between active and passive immunity

Answer 8

1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells / memory cells;
3. Passive involves antibody introduced into body from outside
4. Active long term, because antibody produced in response to antigen
5. Passive short term, because antibody (given) is broken down;
6. Active (can) take time to develop, passive fast acting.

Question 9

5 marks

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how

Answer 9

1. Vaccine contains antigen from pathogen
2. Macrophage presents antigen on its surface
3. T cell with complementary receptor protein binds to antigen;
4. T cell stimulates B cell
5. (With) complementary antibody on its surface
6. B cell secretes large amounts of antibody
7. B cell divides to form clone all secreting / producing same antibody.

Question 10

3 marks

Desribe 3 functions of the golgi apparatus

Answer 10

1. Modifies and packages proteins
2. Modifies and packages lipids
3. Makes lysosomes

Question 11

How does passive immunity work

Answer 11

Passive involves antibody introduced into body from external source
Adding the antibody would cause agglutination and increase efficiency of phagocytosis

Question 12

The human papilloma virus contains a double-stranded DNA genome.
Which components are found in a human papilloma virus? Choose one
* Capsid and attachment protein
* Capsid, attachment protein and reverse transcriptase
* Capsule and attachment protein
* Cell-surface membrane and attachment protein

Answer 12

Capsid and attachment protein

Question 13

5 marks

Outline the similarities in, and the differences between, the structures of chloroplasts and mitochondria.

Answer 13

Similarities
1. Double membrane;
2. Both contain (circular) DNA;
3. Both contain ribosomes;
Differences
4. Thylakoids/lamellae/grana v cristae;
5. Stroma v matrix;
7. Starch grains v no starch grains;

Question 14

2 marks

Suggest how Streptococcus bacteria with a thicker capsule are more likely to survive and so cause lung disease.

Answer 14

Phagocytes less likely to bind to murein in cell wall
This decreases pahgocytosis as theres more binary fission

Question 15

3 marks

Explain why phospholipids can form a bilayer but triglycerides cannot.

Answer 15

• Phospholipid both hyrdophillic and hydrophobic
• Triglycerides only hydrophillic
• Hydrophillic phosphate head attracted to water

Question 16

Explain why the damage to the cells lining the ileum reduces the absorption of the products of digestion and why this reduces absorption of water

Answer 16

Surface area reduces
Less digestion enter cells
Water potential in cell doesnt decrease
So less water enter cells by osmosis

Question 17

State one role of a helper T cell.

Answer 17

Stimulating cytotoxic T cells
Stimulating B cells
Stimulating phagocytes;

Question 18

2 marks

Explain why viruses are described as acellular and non-living.

Answer 18

1. Accelular= not made up of cells
2. Non living= no metabolic reactions/ need a host cell to replicate

Question 19

Give one reason why antibiotics are not effective against viruses.

Answer 19

doesnt have a cell wall

Question 20

The movement of substances across cell membranes is affected by membrane structure. Describe how.

Answer 20

1. Phospholids only allows non-polar, lipid-soulube molecules diffuse across phospholipid bilayer
2. Phospholipid bilayer prevent diffusion of water- solube, polar molecules across membrane
3. Carrier proteins allow active transport
4. Carrier proteins and channel proteins allow facilitated diffusion
5. Cholestrol affects rigidty/ fluidity

Question 21

5 marks

Name and describe five ways substances can move across the cell-surface membrane into a cell.

Answer 21

1. Simple diffusion of small/non-polar molecules down a concentration gradient
2. Facilitated diffusion down a concentration gradient via protein carrier and channel
3. Osmosis of water down a water potential gradient
4. Active transport against a concentration gradient via protein carrier using ATP
5. Co-transport of 2 different substances using a carrier protein

Question 22

2 marks

Suggest and explain 2 ways the cell-surface membranes of the cell lining the uterus may be adapted to allow rapid transport of nutrients

Answer 22

1. Memrane folded so large SA
2. Large number of protein channels/ carriers for FD
3. Large number of carrier proteins for active transport
4. Large number of protein channels/ carriers for co-transport

Question 23

3 marks

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3. NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell. Use your knowledge of transport across cell membranes to suggest how NHE3 does this.

Answer 23

1. Co-transport
2. Uses hydrolysis of ATP
3. Sodium ion and proton bind to protein
4. Protein changes shape to move sodium ion and proton across the membrane

Question 24

2 marks

Bacteria are often used in industry as a source of enzymes. One reason is because bacteria divide rapidly, producing a large number of them in a short time.
Describe how bacteria divide.

Answer 24

1. Binary fission
2. Replication of circular DNA
3. Division of cytoplasm to produce 2 daughter cells
4. Each with a single copy of circular DNA

Question 25

# 3 marks Describe how phagocytosis of a virus leads to presentation of its antigens

Answer 25

1. Phagosome/ vesicle fuses with lysosome 2. Virus destroyed by lysozymes/ hydrolytic enzymes 3. Antigen from virus are displayed on the cell membrane

Question 26

# 3 marks Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen

Answer 26

1. T helper cell receptor binds to antigen on the antigen- presenting cell 2. T helper cell stimulates a specific B cell 3. B cell divides by mitosis 4. Forms plasma cells that release antibodies

Question 27

# 3 marks Describe viral replication

Answer 27

1. Attachment proteins attach to receptors 2. Viral nucleic acid enters cell 3. Reverse transcriptase converts RNA to DNA 4. Cell produces viral proteins 5. Virus assembled and released from cell

Question 28

# 2 marks The scientists broke open the cells to produce a suspension of cell contents. Describe how the scientists would remove large organelles from this suspension of cell contents.

Answer 28

1. Centrifuge at low speeds 2. Large/dense organelles removed in first pellet

Question 29

Use your knowledge of membrane structure to explain the results in absorbance * E – Ethanol, water and acid (greatest absorbance) * F – Ethanol and water (2nd) * G – Water (lowest absorbance)

Answer 29

1. Higher absorbance indicates more pigment 2. More membrane permeability results in more pigment release 3. E and F greater than water because phospholipids dissolve in ethanol 4. E greater than F because acid denatures membrane proteins

Question 30

# Cyclin D undergoes DNA replication faster Some tumour cells contain higher than normal concentrations of cyclin D. Suggest why higher than normal concentrations of cyclin D could result in a tumour.

Answer 30

1. Shortens interphase/ DNA replication starts faster 2. Uncontrolled cell division 3. Resulting in a mass of abnormal cells

Question 31

# 4 maarks Describe how a sample of chloroplasts could be isolated from leaves

Answer 31

1. Break open cells/ homogenise and filter 2. In cold, isotonic, buffered solution 3. Centrifuge and remove nuclei (nucleus removed in first pellet, filter supernatant) 4. Centrifuge higher speed, chloroplasts settle out

Question 32

Explain interphase

Answer 32

* Increase in volume of cell * DNA replication * Organelles replication * Energy stores increase (ATP, protein synthesis)

Question 33

Explain prophase

Answer 33

* Chromosomes condense and become visible * Nuclear envelope disappears

Question 34

Explain metaphase

Answer 34

* Chromosomes arrange themselves at the equator of the cell * Spindle fibres attach to centromere

Question 35

Explain anaphase

Answer 35

* Centromeres divide * Spindle fibres contracts/ shortens * One of each sister chromatid pulled to poles of the cell

Question 36

Explain telophase

Answer 36

* Chromosomes uncoil * Spindle fibres disintegrates * Nuclear envelope reforms

Question 37

Explain cytokineses

Answer 37

* Cytoplasm splits * Cell membrane forms between 2 cells

Question 38

# 1 mark Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time

Answer 38

Form / replace cells quickly / rapidly / divide / multiply / replicate rapidly

Question 39

# 2 marks Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer.

Answer 39

1. Prevents DNA replication / mitosis 2. Nucleotides not joined together

Question 40

# 5 marks Name and describe five ways substances can move across the cell-surface membrane into a cell.

Answer 40

1. Simple diffusion of small, non-polar molecules down a concentration gradient 2. Facilitated diffusion down a concentration gradient via carrier or channel protein 3. Osmosis of water down a water potential gradient 4. Active transport against a concentration gradient via protein carrier using ATP 5. Co-transport of 2 different substances using a carrier protein

Question 41

# 3 marks Describe the processes of facilitated diffusion and active transport

Answer 41

1. Movement of polar/charged molecules 2. Facilitated diffusion movement down a concentration gradient via carrier/channel protein 3. Active transport movement against a concentration gradient via carrier protein using ATP

Question 42

# 6 marks Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue.

Answer 42

1. Homogenise to break open cells 2. Filter to remove debris 3. Cold solution to prevent enzyme activity 4. Isotonic solution to prevent osmosis 5. Buffered solution to stop enzymes/protein denaturing 6. Centrifuge lower speed so nuclei in pellet/move to bottom

Question 43

# 5 marks Describe the role of organelles in the production and release of enzymes by animal cells. Do not include details of transcription in your answer.

Answer 43

1. DNA in nucleus codes for enzyme/protein production 2. Ribosomes/rough endoplasmic reticulum produce proteins 3. Smooth endoplasmic reticulum transports/modifies/processes protein 4. Mitochondria produce ATP 5. Golgi apparatus modifies and packages proteins 6. Vesicles move protein to cell-surface membrane

Question 44

# 1 mark There is currently no effective vaccine available for HIV. Suggest one reason why.

Answer 44

1. (High rate of) mutation 2. (High) genetic diversity 3. HIV in cells could (still) spread infection 4. HIV (DNA) embeds/inserts itself in host DNA 5. Lack of funding/money (for research/development) 6. HIV causes fewer T cells, so immune response (to the vaccine) does not happen

Question 45

# 1 mark Explain how the stain allowed the doctor to count the white blood cells amongst all the red blood cells.

Answer 45

White cells have a nucleus that stains but red cells do not