AQA GCSE (9-1) Biology: Animal Tissues, Organs, and Organ Systems

Key Takeaways Animal Tissues, Organs, and Organ Systems

1. Levels of Organisation in Multicellular Organisms

• Hierarchy:
  Cells → Tissues → Organs → Organ Systems → Organism.
  • Example:
    • Cell: Muscle cell.
    • Tissue: Muscle tissue.
    • Organ: Heart.
    • Organ System: Circulatory system.
    • Organism: Human.
• Tip: Use the mnemonic “Cats Take Orange Oranges Often” to remember the order.

2. The Human Digestive System

• Key Organs and Functions:OrganFunctionSalivary GlandsProduce saliva containing amylase (breaks down starch → glucose).StomachReleases protease (digests proteins) and HCl (kills pathogens, pH 2-3).LiverProduces bile (emulsifies fats, neutralises stomach acid).PancreasProduces carbohydrases, proteases, and lipases.Small IntestineAbsorbs nutrients via villi (increase surface area).Large IntestineAbsorbs water; forms faeces.
• Adaptations:
  • Villi have a large surface area, thin walls, and rich blood supply for efficient absorption.
  • Peristalsis: Rhythmic muscle contractions move food through the digestive tract.
    • Model tip: Imagine pushing a tennis ball through tights by squeezing behind it.

3. Enzymes in Digestion

• Enzyme Types and Reactions:EnzymeSubstrateProductsLocationAmylaseStarchGlucoseMouth (saliva), pancreas.ProteaseProteinsAmino acidsStomach, pancreas.LipaseLipids (fats)Fatty acids + glycerolPancreas.
• Lock and Key Hypothesis:
  • Enzymes have an active site that fits a specific substrate (like a key in a lock).
  • Denaturing: Extreme pH/temperature changes the active site’s shape → enzyme stops working.
    • Example: Boiling amylase denatures it → no starch digestion.
• Graph Interpretation:
  • Optimum temperature/pH = peak enzyme activity.
  • Activity drops sharply if denatured (e.g., at high temperatures).

4. Circulatory System

• Heart Structure:
  • Double Circulation: Blood passes through the heart twice per circuit.
    • Pulmonary circuit: Heart → Lungs → Heart.
    • Systemic circuit: Heart → Body → Heart.
  • Chambers:
    • Atria (upper, thin-walled) receive blood.
    • Ventricles (lower, thick-walled) pump blood.
    • Tip: The left ventricle has the thickest wall (pumps blood to the body).
• Blood Vessels:VesselFunctionAdaptationsArteryCarries blood away from the heartThick muscular/elastic walls (high pressure).VeinReturns blood to the heartThin walls, valves (prevent backflow).CapillaryExchange of substances with tissuesOne-cell thick walls (short diffusion path).
• Blood Components:ComponentFunctionRed Blood CellsCarry oxygen (haemoglobin → oxyhaemoglobin).White Blood CellsFight pathogens (phagocytes engulf, lymphocytes produce antibodies).PlateletsClot blood (form fibrin mesh).PlasmaCarries nutrients (glucose), hormones, CO₂.

5. Health Issues and Disease

• Coronary Heart Disease (CHD):
  • Causes: Atherosclerosis (fatty deposits in arteries), smoking, high cholesterol.
  • Treatments:
    • Stents (mesh to widen arteries) vs. Bypass (vein graft).
    • Tip: Stents are less invasive → faster recovery.
• Cancer:
  • Malignant tumours spread (metastasis); benign do not.
  • Risk Factors: Smoking (carcinogens), UV radiation, HPV.
  • Treatments: Chemotherapy (drugs), radiotherapy (X-rays).
• Lifestyle Risks:
  • Correlation vs. Causation:
    • Causation: Smoking causes lung cancer.
    • Correlation: Obesity is linked to type 2 diabetes (but not the sole cause).

6. Required Practicals

• Food Tests:TestReagentPositive ResultStarchIodineBlue-black colour.GlucoseBenedict’s + heatBrick-red precipitate.ProteinBiuretLilac/purple colour.LipidsEthanol + waterCloudy emulsion.
• Enzyme Experiments:
  • Effect of pH on Amylase: Use buffer solutions; iodine detects starch remaining.
  • Graph tip: Plot rate of reaction (1/time) against pH to find optimum.

7. Key Tips for Exams

1. Diagrams: Draw and label the digestive system/heart (annotate adaptations).
2. Mnemonics:
   • Blood flow: “Left Atrium Lets Oxygenated blood Vent” (LA → LV → Aorta).
3. Avoid Errors:
   • Enzymes: Don’t say “enzymes die” → use “denatured”.
   • Arteries/Veins: Arteries carry blood away from the heart (except pulmonary artery).
4. Past Papers: Practice analysing graphs (e.g., enzyme activity) and evaluating models (e.g., lock and key).

Equations:

• Enzyme reactions:
  • Starch + Amylase → Glucose:
    Starch→AmylaseGlucoseStarchAmylase​Glucose

By mastering these concepts and practising application, you’ll ace your GCSE Biology exams! 🧠📚

50 GCSE Biology Questions on Animal Tissues, Organs, and Organ Systems

Levels of Organisation (5 Questions)

1. Name the five levels of organisation in multicellular organisms.
2. Give an example of an organ system and its function.
3. What is the difference between a tissue and an organ?
4. Provide two examples of tissues found in humans.
5. Explain why cells are considered the “basic building blocks” of life.

Digestive System (10 Questions)

6. Describe the role of the salivary glands in digestion.
7. Why does the stomach produce hydrochloric acid?
8. What is the function of bile, and where is it stored?
9. Explain how villi in the small intestine are adapted for absorption.
10. What is peristalsis, and where does it occur?
11. Name the enzyme produced by the pancreas that breaks down lipids.
12. How does the large intestine contribute to digestion?
13. Why is the small intestine longer than the large intestine?
14. What happens to food that is not digested in the small intestine?
15. Define defecation and name the organ responsible for it.

Enzymes (10 Questions)

16. What is an enzyme?
17. Explain the lock and key hypothesis using amylase as an example.
18. Name the enzyme that breaks down proteins in the stomach.
19. Why does denaturing an enzyme stop it from working?
20. What is the optimum pH for pepsin, and why?
21. How does bile assist lipase in fat digestion?
22. Write the word equation for the breakdown of starch by amylase.
23. Why are enzymes described as biological catalysts?
24. What happens to enzyme activity at temperatures below the optimum?
25. Explain why amylase cannot digest lipids.

Circulatory System (10 Questions)

26. Why is the heart described as a double pump?
27. Name the blood vessel that carries deoxygenated blood to the lungs.
28. What is the function of the coronary arteries?
29. Explain why the left ventricle has a thicker muscular wall than the right.
30. Describe the pathway of blood from the right atrium to the aorta.
31. What is the role of valves in the heart?
32. How are arteries adapted to withstand high blood pressure?
33. Why do veins have valves, but arteries do not?
34. What substance in red blood cells binds to oxygen?
35. How do capillaries facilitate gas exchange in tissues?

Blood Components (5 Questions)

36. List the four main components of blood.
37. What is the function of haemoglobin?
38. How do white blood cells protect the body from pathogens?
39. Describe the role of platelets in blood clotting.
40. What is the difference between oxyhaemoglobin and haemoglobin?

Health Issues & Disease (5 Questions)

41. Define atherosclerosis and name two risk factors.
42. What is a stent, and how does it treat coronary heart disease?
43. Explain how smoking increases the risk of lung cancer.
44. What is the difference between correlation and causation in disease?
45. How does a balanced diet reduce the risk of type 2 diabetes?

Cancer (3 Questions)

46. Distinguish between malignant and benign tumours.
47. Name two methods used to screen for cancer.
48. Why can chemotherapy cause side effects like hair loss?

Practical Experiments (2 Questions)

49. Describe how to test a food sample for glucose.
50. In an experiment to test the effect of pH on amylase activity, why is iodine solution used?

Detailed Answers

1. Cells → Tissues → Organs → Organ Systems → Organism
   • Example: Muscle cell → Muscle tissue → Heart → Circulatory system → Human.
2. Organ System: Digestive system; Function: Breaks down food for absorption.
3. Tissue: Group of similar cells (e.g., nervous tissue).
   Organ: Group of tissues performing a function (e.g., brain).
4. Examples: Nervous tissue, muscle tissue.
5. Cells perform life processes (e.g., respiration) and form all structures.
6. Salivary glands produce saliva containing amylase to digest starch into glucose.
7. HCl creates acidic pH for protease enzymes and kills pathogens.
8. Bile emulsifies fats (breaks them into droplets); stored in the gall bladder.
9. Villi adaptations:
   • Large surface area (many villi).
   • Thin walls (one-cell thick) for short diffusion path.
   • Rich blood supply (capillaries).
10. Peristalsis: Rhythmic muscle contractions moving food through the digestive tract; occurs in the oesophagus and intestines.
11. Lipase (breaks lipids → fatty acids + glycerol).
12. Large intestine absorbs water and salts; forms faeces.
13. Longer length increases surface area for nutrient absorption.
14. Undigested food (e.g., fibre) passes to the large intestine for water absorption.
15. Defecation: Removal of faeces via the anus.
16. Enzyme: Biological catalyst (protein) that speeds up chemical reactions.
17. Lock and Key: Amylase’s active site (lock) binds to starch (key), breaking it into glucose.
18. Protease (e.g., pepsin in the stomach).
19. Denaturing changes the enzyme’s active site shape → substrate no longer fits.
20. Optimum pH for pepsin = 2–3 (matches stomach acid).
21. Bile emulsifies fats → larger surface area for lipase to act.
22. Starch→AmylaseGlucoseStarchAmylase​Glucose
23. They speed up reactions without being used up.
24. Activity decreases due to slower molecular collisions (low kinetic energy).
25. Enzymes are specific; amylase’s active site only fits starch, not lipids.
26. Blood passes through the heart twice per circuit (pulmonary and systemic).
27. Pulmonary artery.
28. Coronary arteries supply oxygenated blood to the heart muscle.
29. Left ventricle pumps blood to the entire body (requires more force).
30. Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium → Left ventricle → Aorta.
31. Valves prevent backflow of blood.
32. Artery adaptations: Thick muscular/elastic walls to withstand high pressure.
33. Veins have valves to ensure blood flows toward the heart against gravity.
34. Haemoglobin in red blood cells binds to oxygen.
35. Capillaries have thin walls (one-cell thick) for efficient diffusion.
36. Blood components: Red blood cells, white blood cells, platelets, plasma.
37. Haemoglobin binds oxygen to form oxyhaemoglobin.
38. White blood cells:

• Phagocytes engulf pathogens.
• Lymphocytes produce antibodies.

39. Platelets release clotting factors → fibrin mesh forms a scab.
40. Oxyhaemoglobin = haemoglobin + oxygen (bright red); haemoglobin = no oxygen (dark red).
41. Atherosclerosis: Fatty deposits in arteries; risks include smoking, high cholesterol.
42. Stent: Mesh tube inserted into arteries to keep them open; less invasive than bypass.
43. Smoking introduces carcinogens (e.g., tar) → DNA mutations → cancer.
44. Causation: Direct cause (e.g., smoking → lung cancer).
    Correlation: Linked but not causal (e.g., obesity linked to diabetes).
45. Balanced diet maintains healthy weight → cells respond better to insulin.
46. Malignant: Spreads (metastasis); Benign: Localised, non-cancerous.
47. Screening methods: Mammograms (breast), smear tests (cervical).
48. Chemotherapy drugs target rapidly dividing cells (cancer + hair follicles).
49. Glucose test:

• Add Benedict’s reagent to food sample.
• Heat in water bath (80°C).
• Positive result: Brick-red precipitate.

50. Iodine detects starch remaining; blue-black colour indicates starch presence.

Need more practice? Try past papers and flashcards! 📝🔬