Key Concepts in BiologyEdexcel GCSE Biology: Topic test

20 questions, 54 marks

Edexcel GCSE Biology

Key Concepts in Biology topic test

Total 54 marks

Name

Class

Date

1
A biologist examines cells lining the trachea (windpipe) of a mammal. The cells have hair-like structures beating on their surface, and are packed closely together, with nearby goblet cells releasing a sticky secretion that traps dust and bacteria breathed in with air.
(a)
What is the name of the hair-like structures found on the surface of the cells lining the trachea?
[1 mark]
ACilia
BFlagella
CVilli
DMicrovilli
(b)
What is the main function of the goblet cells' sticky secretion in the trachea?
[1 mark]
AProducing enzymes to digest trapped bacteria
BTrapping dust and pathogens breathed in with air so cilia can move them away from the lungs
CAbsorbing oxygen from the air into the blood
DProducing antibodies against inhaled pathogens
(c)
Ciliated epithelial cells are described as specialised cells. Explain two ways their structure adapts them to move mucus across the surface of the trachea.
[2 marks]
Total for question 1: 4 marks
2
A student is investigating digestive enzymes. She adds a small piece of egg white (protein) to a test tube containing the protease enzyme pepsin, and a second identical piece of egg white to a test tube containing the carbohydrase enzyme amylase, both kept at the same temperature and pH. After 30 minutes, the egg white in the pepsin tube has partly broken down, but the egg white in the amylase tube is unchanged.
(a)
Why does amylase fail to break down the protein in egg white?
[1 mark]
AAmylase is denatured at the temperature used
BAmylase only works below pH 2
CAmylase's active site is a shape complementary only to carbohydrate substrates, not protein
DAmylase requires light energy to function
(b)
What term describes the fact that pepsin will break down egg white protein but not, for example, starch?
[1 mark]
AEnzyme denaturation
BActive transport
COsmosis
DEnzyme specificity
(c)
Using the idea of the active site, explain why pepsin can break down the protein in egg white but cannot break down starch.
[2 marks]
Total for question 2: 4 marks
3
A student places three identical dialysis tubing bags, each containing the same concentrated sugar solution, into three beakers of distilled water at different temperatures: 10 degrees C, 25 degrees C and 40 degrees C. Each bag is weighed before being placed into its beaker, and then reweighed after 20 minutes. The bag placed in the 40 degrees C beaker gains the most mass; the bag placed in the 10 degrees C beaker gains the least mass.
(a)
Explain, in terms of the movement of water molecules, why the dialysis bags gain mass when placed in distilled water.
[3 marks]
(b)
Explain why the bag in the 40 degrees C beaker gained more mass in 20 minutes than the bag in the 10 degrees C beaker, and suggest one variable, other than temperature, that the student should have controlled to make this a fair test.
[4 marks]
Total for question 3: 7 marks
4
During digestion, amylase in the small intestine breaks down starch in a meal into glucose. Measurements show that the concentration of glucose inside the cells lining the small intestine is often higher than the concentration of glucose remaining in the gut (lumen), yet glucose continues to move from the gut into these cells.
(a)
Explain how amylase breaks down starch into glucose, and explain why an increase in temperature above the enzyme's optimum would reduce the rate at which starch is digested.
[6 marks]
(b)
Explain how glucose produced by the digestion of starch continues to move into the cells lining the small intestine even when its concentration inside those cells is higher than in the gut, and explain why this process requires the cell to use energy from respiration.
[6 marks]
Total for question 4: 12 marks
5
A scientist compares two plant cells taken from the same tomato plant: a cell from the leaf's mesophyll layer, which contains many green, oval organelles, and a cell from the root tip, which contains none of these green organelles but does contain a nucleus, cell membrane, cell wall and mitochondria.
(a)
What is the name of the green, oval organelles found in the leaf mesophyll cell but not in the root tip cell?
[1 mark]
AChloroplasts
BMitochondria
CRibosomes
DNuclei
(b)
Why would chloroplasts not be useful to a cell in the root tip?
[1 mark]
ARoot tip cells do not need a cell wall
BRoot tip cells are underground and receive little or no light, so cannot photosynthesise
CRoot tip cells lack mitochondria
DRoot tip cells cannot divide
(c)
Both the leaf mesophyll cell and the root tip cell contain mitochondria. Explain why both cell types need mitochondria, even though only one carries out photosynthesis.
[2 marks]
Total for question 5: 4 marks
6
A technician investigates the activity of lipase, an enzyme that breaks down fats, at three different pH values: pH 2, pH 7 and pH 9. She mixes lipase with a fat substrate at each pH and measures how quickly the fat is broken down, keeping temperature and substrate concentration constant. Lipase shows almost no activity at pH 2, high activity at pH 7, and reduced activity at pH 9.
(a)
What term describes the pH at which lipase shows its highest activity?
[1 mark]
ANeutral point
BIsoelectric pH
COptimum pH
DDenaturing pH
(b)
What is the most likely explanation for lipase showing almost no activity at pH 2?
[1 mark]
AAt pH 2 there is not enough fat substrate available
BLipase only works above 25 degrees C
CLipase is destroyed by oxygen at low pH
DThe very low pH has changed the shape of the active site so the substrate no longer fits, denaturing the enzyme
(c)
Explain why lipase shows reduced activity at pH 9 compared with pH 7, in terms of the enzyme's active site.
[2 marks]
Total for question 6: 4 marks
7
A student cuts five identical cylinders of apple tissue, weighs each one, then places them into salt solutions of different concentrations for 30 minutes: 0%, 0.2 mol/dm3, 0.4 mol/dm3, 0.6 mol/dm3 and 0.8 mol/dm3. She then removes each cylinder, blots it dry and reweighs it. The cylinder placed in 0% salt solution has an initial mass of 3.20 g and a final mass of 3.68 g. The cylinder placed in 0.8 mol/dm3 salt solution has an initial mass of 3.10 g and a final mass of 2.48 g.
(a)
Calculate the percentage change in mass of the apple cylinder placed in the 0% salt solution. Show your working and state whether this is a percentage gain or loss.
[3 marks]
(b)
Calculate the percentage change in mass of the apple cylinder placed in the 0.8 mol/dm3 salt solution, and explain, in terms of the concentration of water in and around the cells, why this cylinder changed mass in the opposite direction to the cylinder placed in 0% salt solution.
[4 marks]
Total for question 7: 7 marks
8
A biologist compares two spherical single-celled organisms living in the same pond water. Organism P has a radius of 10 micrometres. Organism Q has a radius of 30 micrometres. Both organisms obtain all the oxygen they need by diffusion directly across their cell membrane, and both have the same rate of oxygen use per unit of cytoplasm volume.
(a)
Explain, using the ideas of surface area and volume, why organism Q is more likely to struggle to obtain enough oxygen by diffusion than organism P. You do not need to calculate exact surface areas or volumes.
[6 marks]
(b)
Suggest and explain one adaptation organism Q could evolve to increase the rate at which oxygen reaches its cytoplasm by diffusion, using the factors that affect the rate of diffusion.
[6 marks]
Total for question 8: 12 marks

End of questions