AQA A Level Biology 4/5/6
mark questions (2023/2024)
(Certified Answers)
In daylight, most of the water evaporates from the leaves but some is used by the plant.
Describe the ways in which this water could be used by the plant. (6)
1. (water is used in) the light-dependent reactions of photosy...
AQA A Level Biology 4/5/6
mark questions, (Certified
Answers)
Many different substances enter and leave a cell by crossing its cell surface
membrane. Describe how substances can cross a cell surface membrane.
(5)
1 (Simple / facilitated) diffusion from high to low
concentration / down concentration gradient;
2 Small / non-polar / lipid-soluble molecules pass via phospholipids /
bilayer;
OR
Large / polar / water-soluble molecules go through proteins;
3 Water moves by osmosis / from high water potential to low water potential
/ from less to more negative water potential;
4 Active transport is movement from low to high
concentration / against concentration gradient;
5 Active transport / facilitated diffusion involves proteins/carriers;
6 Active transport requires energy / ATP;
7 Ref. to Na+ / glucose co-transport;
Describe and explain how the lungs are adapted to allow rapid exchange of
oxygen between air in the alveoli and blood in the capillaries around them.
(5)
1 Many alveoli / alveoli walls folded provide a large surface area;
2 Many capillaries provide a large surface area;
3 (So) fast diffusion;
________________________________________________
4 Alveoli or capillary walls / epithelium / lining are thin / short distance
between alveoli and blood;
5 Flattened / squamous epithelium;
6 (So) short diffusion distance / pathway;
7 (So) fast diffusion;
________________________________________________
8 Ventilation / circulation;
9 Maintains a diffusion / concentration gradient;
10 (So) fast diffusion;
,Scientists believe that it may be possible to develop vaccines that make
use of microfold cells. Explain how this sort of vaccine would lead to a
person developing immunity to the pathogen (5)
1.Vaccine contains antigen/ dead pathogen
2.Microfold cells take up/bind and present/transport antigen (to immune
system)
3.T-cells activate B-cells
4.B cells divide / undergo mitosis
5.B cells produce antibodies
6.Memory cells produced
7.More antibodies produced faster in secondary response
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Explain the role of B-lymphocytes and T-lymphocytes in the defence of the
body against a virus infection. (6)
1.B lymphocytes produce antibodies/involved in humoral response;
2.T lymphocytes involved in cell mediated immunity;
3.Macrophages present antigens;
4.(specific) B lymphocytes recognise/bind to antigen;
5.increase in numbers by mitosis;
6.produce plasma cells (which make antibodies);
7.antibodies bind to and clump/ agglutinate virus;
8.memory cells produced by 1st exposure/cloned on 2nd exposure;
9.T lymphocytes(helpers) produce 10.lymphokines/chemicals;
11.which aid B lymphocyte cloning;
12.encourages phagocytes to engulf clumped virus;
13.killer T cells kill virus infected cells;
Explain how water enters a plant root from the soil and travels through to
the endodermis. (5)
1. Water enters root hair cells;
2. By osmosis;
3. Because active uptake of mineral ions has crated a water potential
gradient;
4. Water moves through cortex;
5. Down water potential gradient;
6. Through cell vacuoles and cytoplasms (symplastic pathway);
7. And through apoplastic pathway (cell walls);
, 1. Entry of ions leads to a reduced water potential;
2. Water potential established between xylem and surrounding cells;
3. Plasma membranes of surroudning cells are partially permeable;
4. Water enters xylem by osmosis;
5. Volume of water in xylem increases;
6. Cannot move back due to gradient;
7. Pressure in xylem increases and forces water upwards.
The presence of an air bubble in a xylem vessel in the stem blocks the
movement through that vessel. Use the cohesion-tension theory to explain
why. (4)
1. Evaporation from leaves (transpiration);
2. Water in xylem under tension (pulled up);
3. Because water molecules cohere (stick together) (because of hydrogen
bonds);
4. So water travels in a single column;
5. A water bubble would break the column;
In daylight, most of the water evaporates from the leaves but some is used
by the plant. Describe the ways in which this water could be used by the
plant. (6)
1. (water is used in) the light-dependent reactions of photosynthesis;
2. electrons from water enable ATP production / H+ are used to reduce
NADP / produces O2;
3. (water can be used in) hydrolysis reactions within the plant;
4. to create turgor;
5. as a solvent for transport;
6. as a medium for chemical reactions;
7. component of cells / cytoplasm;
Describe two features you would expect in the leaves of a tree adapted to a
dry environment. Explain how each feature helps the tree's survival. (6)
Sunken stomata;
water evaporation into pit creates local humidity;
increased humidity reduces gradient for water evaporation;
close arrangement of stomata;
diffusion shells of individual stomata overlap;
interferes with water diffusion and slows evaporation;
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