Transport, Excretion and the Nervous System

What to remember

• The human heart has four chambers and pumps blood in a double circulation. Arteries carry blood away from the heart; veins carry blood to the heart. Plants use xylem for water and phloem for food.
• The kidney is the main excretory organ. Its unit is the nephron. Blood is filtered, useful substances are reabsorbed, and urine carries urea and extra water out.
• The nervous system works by electrical impulses through neurons; hormones coordinate more slowly. The brain has the cerebrum, cerebellum and medulla. Plants use hormones such as auxin and gibberellin.

Blood and blood vessels

Blood is a fluid connective tissue.

RBCs are made in bone marrow. In adults, normal blood pressure is about 120/80 mm Hg (systolic/diastolic).

Blood groups (ABO): A, B, AB, O. Group O is the universal donor (no A or B antigen); AB is the universal recipient. Rh factor is another antigen. Karl Landsteiner discovered the ABO groups.

The heart and circulation

The human heart lies in the chest, slightly to the left. It has two upper chambers (atria or auricles) and two lower chambers (ventricles). Valves keep blood from flowing backward. The left ventricle has the thickest wall because it pumps blood to the whole body.

Double circulation

• Pulmonary circulation: right ventricle → lungs → left atrium (blood gets oxygen).
• Systemic circulation: left ventricle → body → right atrium.

Fish have a two-chambered heart. Amphibians and most reptiles have a three-chambered heart. Birds and mammals have four chambers. Normal heart rate is about 72 beats per minute at rest. The pacemaker (SA node) starts each beat.

Lymph is a colourless fluid that drains tissue fluid and helps immunity. Lymph nodes filter germs.

Transport in plants

• Xylem carries water and minerals upward from roots to leaves. It has vessels and tracheids; it is dead tissue.
• Phloem carries food (sugar) from leaves to other parts in both directions (translocation). It has sieve tubes and companion cells; it is living tissue.
• Transpiration: loss of water vapour from leaves through stomata. It pulls water up (transpiration pull) and cools the plant.
• Root pressure helps push water up, mainly at night and in small plants. Root hair cells absorb water by osmosis.

In tall forest trees, transpiration pull is the main force raising water to the top.

Excretion

Excretion is removal of metabolic waste. Main wastes: carbon dioxide (lungs), urea and water (kidneys, skin sweat), bile pigments (liver).

Human excretory system: a pair of kidneys, two ureters, a urinary bladder and a urethra. Nephron is the functional unit (about a million per kidney).

Urine formation

• 1. Ultrafiltration: blood is filtered in the glomerulus, inside Bowman's capsule.
• 2. Selective reabsorption: glucose, amino acids, salts and much water return to blood in the tubule.
• 3. Secretion and collection: extra waste is added and urine collects in the collecting duct.

Urine is mainly water with urea, uric acid and salts. When kidneys fail, dialysis (artificial kidney) filters the blood.

Plants remove waste as gases through stomata and lenticels, store it in leaves, bark and fruits, and discard it by leaf fall. Gums, resins and latex are waste products of plants.

Nervous system

Neuron has a cell body (cyton), dendrites (receive impulse), and an axon (carries impulse away). The gap between two neurons is a synapse; chemicals called neurotransmitters cross it.

Divisions

• Central nervous system (CNS): brain and spinal cord.
• Peripheral nervous system: nerves to and from the CNS (cranial and spinal nerves).

The brain is protected by the skull and meninges, with cerebrospinal fluid. The human brain weighs about 1.3–1.4 kg.

Reflex action: a quick, automatic response without thinking, for example pulling the hand from a hot object. Reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle). The spinal cord controls reflexes.

Hormones and coordination

Endocrine glands release hormones directly into blood.

Plant hormones

• Auxin: cell elongation, bending towards light.
• Gibberellin: stem growth, seed germination.
• Cytokinin: cell division, delays ageing of leaves.
• Abscisic acid: growth inhibitor, closes stomata, seed dormancy.
• Ethylene: gas that ripens fruit.

Tropism: phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals). Shoots show positive phototropism and negative geotropism. Roots show positive geotropism and positive hydrotropism.

Extra points for the exam

Functions of blood: transport of oxygen, carbon dioxide, nutrients, hormones and wastes; protection by WBCs and clotting; and regulation of body temperature. The average adult has about 5 litres of blood. Blood is about 7 to 8 per cent of body weight. A normal haemoglobin level helps carry oxygen; low haemoglobin is anaemia.

Heartbeat sounds: the "lub" is the closing of valves between atria and ventricles; the "dub" is the closing of the valves at the exits of the ventricles. A doctor listens with a stethoscope. An ECG records the electrical activity of the heart. The sphygmomanometer measures blood pressure.

Circulatory diseases: hypertension (high blood pressure), atherosclerosis (fat deposits in arteries) and heart attack (blocked supply to heart muscle). Regular exercise and less salt and fat help prevent them.

Cardiac output = heart rate × stroke volume. At 72 beats per minute and 70 mL per beat, output is 5,040 mL per minute, about 5 litres.

Water movement in plants: roots absorb water through root hairs by osmosis. Water moves up the xylem by transpiration pull and root pressure. On hot days stomata may close to cut water loss. In a forest, a single large tree can transpire a very large amount of water; forests therefore influence local humidity and rainfall.

Nervous coordination vs chemical coordination

Sense organs: eyes (sight), ears (hearing and balance), nose (smell), tongue (taste), skin (touch, temperature, pain). In the eye the retina holds rods (dim light) and cones (colour). Vitamin A is needed for rod function.

Autonomic nervous system: controls involuntary actions. Its two parts, sympathetic and parasympathetic, work in opposite ways: the sympathetic raises heart rate in danger; the parasympathetic slows it down at rest.

Excretion related facts: the skin removes water and salts as sweat. The liver changes harmful ammonia into urea. The lungs remove carbon dioxide and some water vapour. Adults pass about 1 to 1.5 litres of urine per day. Urine is light yellow because of a pigment called urochrome.

Exam traps

• 1. Pulmonary artery carries deoxygenated blood, and the pulmonary vein carries oxygenated blood.
• 2. Xylem moves water up; phloem moves food both ways.
• 3. Xylem is dead; phloem is living tissue.
• 4. Cerebellum is for balance; medulla is for involuntary actions.
• 5. Insulin lowers sugar; lack causes diabetes mellitus.
• 6. Reflexes are controlled by the spinal cord, not the brain.
• 7. Kidney reabsorbs useful substances; it does not filter only waste.
• 8. Pituitary is the master gland; thyroid is not.

One-liners

• 1. Heart has four chambers.
• 2. Left ventricle has the thickest wall.
• 3. Group O is the universal donor.
• 4. Normal blood pressure is about 120/80 mm Hg.
• 5. Platelets help in clotting.
• 6. Nephron is the unit of the kidney.
• 7. Urea is the main nitrogen waste in humans.
• 8. Xylem carries water; phloem carries food.
• 9. Neuron's axon carries impulse away from the cell body.
• 10. Cerebellum maintains balance.
• 11. Thyroxine needs iodine.
• 12. Ethylene ripens fruit.

Practice questions

1. How many chambers does the human heart have?

   1. Two
   2. Five
   3. Three
   4. Four
   Answer

   D. Four

   Two atria and two ventricles.

2. Which chamber of the heart has the thickest wall?

   1. Left atrium
   2. Right ventricle
   3. Right atrium
   4. Left ventricle
   Answer

   D. Left ventricle

   It pumps blood to the whole body.

3. Which blood cells carry oxygen?

   1. Platelets
   2. White blood cells
   3. Red blood cells
   4. Plasma cells
   Answer

   C. Red blood cells

   Haemoglobin in RBCs binds oxygen.

4. Platelets help in

   1. carrying oxygen
   2. fighting germs
   3. making bile
   4. blood clotting
   Answer

   D. blood clotting

   They plug wounds.

5. The universal blood donor group is

   1. A
   2. AB
   3. O
   4. B
   Answer

   C. O

   Group O has no A or B antigens.

6. The universal recipient blood group is

   1. A
   2. AB
   3. B
   4. O
   Answer

   B. AB

   AB has no anti-A or anti-B antibodies.

7. The ABO blood groups were discovered by

   1. William Harvey
   2. Edward Jenner
   3. Karl Landsteiner
   4. Robert Koch
   Answer

   C. Karl Landsteiner

   Landsteiner discovered them in 1900.

8. Normal human blood pressure is about

   1. 160/100 mm Hg
   2. 80/120 mm Hg
   3. 60/40 mm Hg
   4. 120/80 mm Hg
   Answer

   D. 120/80 mm Hg

   Systolic over diastolic.

9. Which vessel carries deoxygenated blood from the heart to the lungs?

   1. Aorta
   2. Pulmonary artery
   3. Vena cava
   4. Pulmonary vein
   Answer

   B. Pulmonary artery

   The pulmonary artery is the exception among arteries.

10. Valves are present in

    1. veins
    2. arteries
    3. capillaries only
    4. the aorta wall only
    Answer

    A. veins

    Valves prevent backflow in veins.

11. Exchange of materials between blood and tissues occurs in

    1. veins
    2. arteries
    3. lymph nodes
    4. capillaries
    Answer

    D. capillaries

    Their walls are one cell thick.

12. A fish heart has

    1. four chambers
    2. three chambers
    3. two chambers
    4. one chamber
    Answer

    C. two chambers

    Fish have one atrium and one ventricle.

13. The natural pacemaker of the heart is the

    1. aorta
    2. AV valve
    3. pericardium
    4. SA node
    Answer

    D. SA node

    It starts each heartbeat.

14. Water and minerals move up the stem through the

    1. cambium
    2. epidermis
    3. xylem
    4. phloem
    Answer

    C. xylem

    Xylem carries water upward.

15. Food made in leaves is carried to other parts by the

    1. root hairs
    2. phloem
    3. stomata
    4. xylem
    Answer

    B. phloem

    This is translocation.

16. Loss of water vapour from the leaves is called

    1. translocation
    2. transpiration
    3. respiration
    4. guttation only
    Answer

    B. transpiration

    It pulls water up the plant.

17. Which plant tissue is made of living cells?

    1. Dead fibres
    2. Xylem vessels
    3. Tracheids
    4. Phloem
    Answer

    D. Phloem

    Xylem vessels are dead; sieve tubes of phloem are living.

18. The functional unit of the kidney is the

    1. villus
    2. alveolus
    3. nephron
    4. neuron
    Answer

    C. nephron

    There are about a million in each kidney.

19. Ultrafiltration of blood takes place in the

    1. urinary bladder
    2. urethra
    3. ureter
    4. glomerulus
    Answer

    D. glomerulus

    Blood is filtered into Bowman's capsule.

20. The main nitrogenous waste of humans is

    1. uric acid
    2. urea
    3. ammonia
    4. creatinine only
    Answer

    B. urea

    Humans are ureotelic.

21. Birds and insects excrete nitrogenous waste mainly as

    1. carbon dioxide
    2. urea
    3. uric acid
    4. ammonia
    Answer

    C. uric acid

    Uric acid saves water.

22. An artificial kidney is used for

    1. dialysis
    2. respiration
    3. transpiration
    4. digestion
    Answer

    A. dialysis

    It filters the blood in kidney failure.

23. Plants get rid of waste by

    1. dialysis
    2. urination
    3. leaf fall
    4. sweating
    Answer

    C. leaf fall

    They store wastes in leaves and bark and shed them.

24. The part of a neuron that carries impulses away from the cell body is the

    1. axon
    2. synapse
    3. dendrite
    4. nucleus
    Answer

    A. axon

    Dendrites receive impulses.

25. The gap between two neurons is called a

    1. axon
    2. node
    3. cyton
    4. synapse
    Answer

    D. synapse

    Neurotransmitters cross it.

26. Which part of the brain controls balance and posture?

    1. Cerebrum
    2. Cerebellum
    3. Medulla
    4. Hypothalamus
    Answer

    B. Cerebellum

    The cerebellum coordinates movement.

27. Heartbeat, breathing and blood pressure are controlled by the

    1. cerebrum
    2. spinal cord
    3. medulla oblongata
    4. cerebellum
    Answer

    C. medulla oblongata

    These are involuntary actions.

28. A quick automatic response such as pulling a hand from fire is called

    1. voluntary action
    2. reflex action
    3. growth
    4. reproduction
    Answer

    B. reflex action

    It is controlled by the spinal cord.

29. The 'master gland' of the body is the

    1. pituitary
    2. adrenal
    3. thyroid
    4. pancreas
    Answer

    A. pituitary

    It controls many other glands.

30. Lack of iodine in the diet causes

    1. rickets
    2. diabetes
    3. anaemia
    4. goitre
    Answer

    D. goitre

    Thyroxine needs iodine.

31. Insulin is secreted by the

    1. kidney
    2. liver
    3. pancreas
    4. thyroid
    Answer

    C. pancreas

    Lack of insulin causes diabetes.

32. Which plant hormone ripens fruits?

    1. Ethylene
    2. Gibberellin
    3. Auxin
    4. Cytokinin
    Answer

    A. Ethylene

    Ethylene is a gas.

33. Which plant hormone promotes cell elongation and bending towards light?

    1. Cytokinin
    2. Auxin
    3. Ethylene
    4. Abscisic acid
    Answer

    B. Auxin

    Auxin collects on the shaded side.

34. The growth of a shoot towards light is

    1. negative phototropism
    2. hydrotropism
    3. positive geotropism
    4. positive phototropism
    Answer

    D. positive phototropism

    Shoots grow towards light.

35. Roots growing downward show

    1. phototropism
    2. positive geotropism
    3. negative geotropism
    4. negative hydrotropism
    Answer

    B. positive geotropism

    Roots grow toward gravity.

36. The heart of a person beats about 72 times per minute at rest. How many beats occur in 10 minutes?

    1. 720
    2. 7,200
    3. 360
    4. 72
    Answer

    A. 720

    72 × 10 = 720.

37. If the heart pumps 70 mL of blood per beat at 72 beats per minute, the output per minute is about

    1. 50,400 mL
    2. 504 mL
    3. 1,440 mL
    4. 5,040 mL
    Answer

    D. 5,040 mL

    70 × 72 = 5,040 mL.

38. A person's blood pressure is 120/80 mm Hg. The pulse pressure (systolic − diastolic) is

    1. 200 mm Hg
    2. 80 mm Hg
    3. 40 mm Hg
    4. 120 mm Hg
    Answer

    C. 40 mm Hg

    120 − 80 = 40.

39. Statements: 1. Arteries always carry oxygenated blood. 2. Veins have valves. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    The pulmonary artery carries deoxygenated blood.

40. Statements: 1. Xylem moves water upward only. 2. Phloem moves food in both directions. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are true.

41. Statements: 1. Reflexes are controlled mainly by the spinal cord. 2. Reflexes need thinking in the cerebrum. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Reflexes bypass thinking.

42. Statements: 1. The kidney reabsorbs glucose. 2. Urine formation involves ultrafiltration. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are true.

43. Statements: 1. Group AB is the universal donor. 2. Group O has no A or B antigens. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    O is the universal donor.

44. Statements: 1. Thyroxine contains iodine. 2. Adrenaline prepares the body for emergency. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are true.

45. Statements: 1. Mammals and birds have four-chambered hearts. 2. Amphibians have four-chambered hearts. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Amphibians have three chambers.