O Level Biology Practice Paper 1

TuitionGoWhere Practice Paper - Biology O-Level - Answer Key

Total Marks: 80

Section A [20 marks]

1. (a) Organelle identification [2]

(i) Name the organelle labeled A that is responsible for protein synthesis. [1] Answer: Ribosome / Rough endoplasmic reticulum [1]

(ii) State the function of organelle B in the leaf cell. [1] Answer: Photosynthesis / To trap light energy for photosynthesis [1]

(b) Describe two structural differences between a bacterial cell and the plant cell shown above. [2] Marking scheme: Any two from:

• Bacterial cell has cell wall made of peptidoglycan; plant cell has cell wall made of cellulose [1]
• Bacterial cell has no membrane-bound nucleus; plant cell has membrane-bound nucleus [1]
• Bacterial cell has no chloroplasts; plant cell has chloroplasts [1]
• Bacterial cell has plasmids; plant cell has no plasmids [1]

2. (a) Complete the table [3]

(b) Food test for starch [2] Answer: Test: Iodine solution [1] Positive result: Blue-black color [1]

3. Enzyme investigation [6]

(a) State the optimum pH for amylase activity. [1] Answer: pH 7 [1]

(b) Explain why enzyme activity is very low at pH 2. [3] Marking scheme:

• Low pH denatures the enzyme [1]
• Active site changes shape [1]
• Enzyme-substrate complex cannot form / substrate cannot bind [1]

(c) Name the substrate and product of amylase. [2] Answer: Substrate: Starch [1] Product: Maltose [1]

4. Osmosis investigation [5]

(a) Define the term osmosis. [2] Answer: Movement of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane [2] Award 1 mark for water movement, 1 mark for through partially permeable membrane

(b) (i) State the concentration of the solution that is isotonic to the potato cells. [1] Answer: 10% [1]

(ii) Explain why the potato strip gained mass in the 0% solution. [2] Marking scheme:

• Water moved into potato cells by osmosis [1]
• Because water potential of 0% solution is higher than inside potato cells [1]

Section B [30 marks]

5. Human reproduction [10]

(a) Describe the sequence of events after fertilisation. [6] Marking scheme:

• Zygote divides by mitosis to form embryo [1]
• Embryo travels down fallopian tube/oviduct [1]
• Blastocyst forms and implants in uterine wall/endometrium [1]
• Placenta develops from embryonic and maternal tissues [1]
• Umbilical cord connects fetus to placenta [1]
• Amniotic fluid surrounds and protects developing fetus [1]

(b) Explain how the placenta is adapted for efficient exchange. [4] Marking scheme:

• Large surface area for exchange [1]
• Thin barrier between maternal and fetal blood [1]
• Rich blood supply on both sides [1]
• Allows passage of nutrients, oxygen, and waste products [1]

6. Plant root cells [8]

(a) Explain the advantage of pumping air through nutrient solution. [4] Marking scheme:

• Air provides oxygen [1]
• Oxygen used in aerobic respiration to produce ATP [1]
• ATP provides energy for active transport [1]
• Active transport needed to absorb mineral ions against concentration gradient [1]

(b) (i) Explain how root hair cell structure is adapted. [3] Marking scheme:

• Long projection increases surface area for absorption [1]
• Thin cell wall allows easy passage of water and ions [1]
• Many mitochondria provide ATP for active transport [1]

(ii) Name the process by which mineral ions are absorbed. [1] Answer: Active transport [1]

7. Nervous system and reflexes [8]

(a) Describe how named components produce a reflex action. [6] Marking scheme:

• Sensory receptor detects stimulus [1]
• Sensory neurone transmits impulse to spinal cord [1]
• Relay neurone in spinal cord connects sensory to motor neurone [1]
• Synapse: neurotransmitter released and crosses synaptic cleft [1]
• Motor neurone transmits impulse to effector [1]
• Effector (muscle/gland) responds [1]

(b) Explain why reflex actions are important for survival. [2] Marking scheme:

• Rapid response to danger/harmful stimuli [1]
• Automatic response does not require conscious thought [1]

8. Water regulation [6]

(a) Explain how water intake affects urine concentration. [4] Marking scheme:

• Increased water intake increases blood water potential [1]
• Less ADH released from pituitary gland [1]
• Less water reabsorbed in kidney tubules [1]
• More dilute urine produced [1]

(b) Name the hormone involved in water regulation. [1] Answer: ADH / Antidiuretic hormone [1]

(c) State where this hormone is produced. [1] Answer: Pituitary gland / Hypothalamus [1]

Section C [30 marks]

9. Leaf structure and photosynthesis [14]

(a) (i) Name the process in palisade mesophyll cells. [1] Answer: Photosynthesis [1]

(ii) Write the word equation for this process. [2] Answer: Carbon dioxide + Water → Glucose + Oxygen [2] Award 1 mark for reactants, 1 mark for products

(b) Explain how leaf structure is adapted for gas exchange. [5] Marking scheme:

• Stomata allow gas exchange [1]
• Guard cells control opening and closing of stomata [1]
• Spongy mesophyll has air spaces for gas circulation [1]
• Thin leaf structure reduces diffusion distance [1]
• Large surface area of mesophyll cells for gas exchange [1]

(c) (i) Explain why photosynthesis rate increases from 0 to X. [2] Marking scheme:

• Light is the limiting factor [1]
• More light energy available for photosynthesis [1]

(ii) Explain why rate doesn't increase beyond point X. [2] Marking scheme:

• Light is no longer limiting [1]
• Another factor becomes limiting (temperature/CO₂ concentration) [1]

(iii) State two other limiting factors. [2] Answer: Any two from:

• Temperature [1]
• Carbon dioxide concentration [1]
• Chlorophyll concentration [1]

10. Human digestion [14]

(a) Describe roles of enzymes in digestion with examples. [6] Marking scheme:

• Enzymes act as biological catalysts to speed up digestion [1]
• Amylase breaks down starch to maltose in mouth/small intestine [1]
• Pepsin breaks down proteins to polypeptides in stomach [1]
• Lipase breaks down fats to fatty acids and glycerol in small intestine [1]
• Maltase breaks down maltose to glucose in small intestine [1]
• Trypsin breaks down proteins in small intestine [1] Award maximum 6 marks for enzyme function and specific examples

(b) Explain why stomach produces hydrochloric acid. [3] Marking scheme:

• Provides optimum pH for pepsin activity [1]
• Kills bacteria in food [1]
• Denatures proteins to make them easier to digest [1]

(c) Describe how small intestine is adapted for absorption. [5] Marking scheme:

• Villi increase surface area [1]
• Microvilli further increase surface area [1]
• Thin wall reduces diffusion distance [1]
• Rich blood supply maintains concentration gradient [1]
• Lacteal for fat absorption [1]

11. Active transport [8]

(a) Explain what is meant by active transport. [2] Answer: Movement of substances against concentration gradient using energy from ATP [2] Award 1 mark for against concentration gradient, 1 mark for energy/ATP

(b) Give two examples of active transport. [2] Answer: Any two from:

• Uptake of mineral ions by root hair cells [1]
• Glucose absorption in small intestine [1]
• Sodium-potassium pump in nerve cells [1]

(c) Explain why active transport is important for mineral ion uptake. [4] Marking scheme:

• Mineral ions are often in low concentration in soil [1]
• Plant needs higher concentration inside cells [1]
• Movement against concentration gradient requires energy [1]
• Ensures plant gets essential minerals for growth and metabolism [1]