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2024 AQA A-LEVEL BIOLOGY TOPIC 3 EXAM WITH CORRECT ANSWERS
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2024 AQA A-LEVEL BIOLOGY TOPIC 3 EXAM WITH CORRECT ANSWERS
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2024 AQA A-LEVEL BIOLOGYTOPIC 3 EXAM WITH CORRECT
ANSWERS
Why are Microorganisms able to perform exchange via their surface? -
CORRECT-ANSWERS• have a large surface area to volume ratio
• have a short diffusion distance
• have low demand
How do Microorganisms Obtain Nutrients & Remove Waste? - CORRECT-
ANSWERS• by exchange via their surface
• nutrients (e.g. glucose, oxygen) move in by diffusion via their surface
• waste (e.g. carbon dioxide) move out by diffusion via their surface
What is a Potometer? - CORRECT-ANSWERSapparatus used to measure rate
of transpiration
Principle of potometer? - CORRECT-ANSWERS• as transpiration occurs from
the leaves, the plant will pull up more water from the potometer by
cohesion-tension causing the bubble to move towards the plant
• the more water lost by transpiration, the more water taken up, the further
the bubble moves
Measuring Rate of Transpiration? - CORRECT-ANSWERS• rate of transpiration
= volume of transpiration divided by time
• for volume of transpiration, distance bubble moved x cross-sectional area
of tube (πr2)
How to set up a potometer? - CORRECT-ANSWERS• choose healthy leaf and
shoot
• cut shoot underwater and connect to potometer underwater (prevents air
bubbles entering/blocking xylem)
• ensure potometer is air tight and water tight
What does a potometer actually measure? - CORRECT-ANSWERS• measures
rate of water uptake as a result of water loss from plant
• (water loss can be due to: transpiration, photosynthesis, making cells
turgid, loss from potometer)
, What is a Xerophyte? - CORRECT-ANSWERSa plant adapted to reduce water
loss (reduce transpiration)
Adaptations of Xerophyte? - CORRECT-ANSWERS• spiky, needle like leaves =
reduced surface area
• thick waxy cuticle = waterproof, impermeable barrier
• densely packed spongy mesophyll = less air spaces, less water vapour
build up
• sunken stomata/hairy leaves/rolled up leaves = traps moist layer of air,
reduces concentration gradient
Function of Phloem? - CORRECT-ANSWERStransport organic material (e.g.
Sucrose) up and down a plant
Structure of phloem? - CORRECT-ANSWERSmade of 2 parts (Sieve Tube with
Companion Cells alongside)
How does phloem transport organic material like sucrose? - CORRECT-
ANSWERS1. by principle of Mass Flow (mass flow of water carries the
sucrose)
2. Sucrose loaded into Phloem at Source
3. Hydrogen Ions (H+) actively transported from companion cells into source
4. therefore, H+ diffuses back into companion cells from source
5. as they do, they pull in sucrose with them by co-transport
6. sucrose then diffuses into sieve tube
7. this lowers the water potential of sieve tube so water follows by osmosis
8. this water will carry the sucrose by hydrostatic pressure (mass flow)
9. Sucrose unloaded from Phloem at Sink
10. sucrose moves out of phloem/sieve tube into sink by diffusion
11. water follows by osmosis
Enzymes of Carbohydrate Digestion? - CORRECT-ANSWERS• Starch/Glycogen
(Salivary Amylase in Mouth, Pancreatic Amylase in Small Intestine) into
Maltose
• Maltose (Maltase on lining of Small Intestine) into Glucose
• Lactose (Lactase on lining of Small Intestine) into Glucose and Galactose
• Sucrose (Sucrase on lining of Small Intestine) into Glucose and Fructose
Enzymes of Protein Digestion? - CORRECT-ANSWERS• Endopeptidase (in
stomach), hydrolyses peptide bonds in middle of polypeptide chain into
many smaller chains
• Exopeptidase (in small intestine), hydrolyses peptide bonds at end of
chains to leave dipeptides
• Deipeptidase (on lining of small intestine), hydrolyse dipeptides into amino
acids
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