Coordination: Nervous System and Plant Hormones

What to remember

• Coordination means working together of body parts in response to a stimulus. Animals use the nervous system (fast, by electrical impulses) and the endocrine system (slower, by hormones); plants use hormones.
• The neuron is the unit of the nervous system; the brain and spinal cord form the central nervous system. A reflex action is a quick, automatic response that passes through the spinal cord.
• Plant hormones are auxin, gibberellin, cytokinin, abscisic acid and ethylene. Auxin helps growth and bending towards light; abscisic acid stops growth; ethylene ripens fruits.

Stimulus and response

A stimulus is a change in the surroundings (light, heat, sound, touch, smell, taste). The body part that gets the stimulus is the receptor; the part that responds is the effector (muscle or gland). The path is: receptor → sensory nerve → brain or spinal cord → motor nerve → effector.

The neuron

A neuron (nerve cell) has a cell body (cyton) with the nucleus, short branches called dendrites that receive impulses, and a long axon that carries the impulse away. The axon of many neurons is covered by a fatty myelin sheath. The gap where one neuron meets the next is the synapse; chemicals called neurotransmitters carry the message across it. The impulse flows from dendrite → cell body → axon.

Human nervous system

It has three parts.

• 1. Central nervous system (CNS): brain and spinal cord.
• 2. Peripheral nervous system (PNS): 12 pairs of cranial nerves and 31 pairs of spinal nerves.
• 3. Autonomic nervous system: controls involuntary actions such as heartbeat and digestion. It has the sympathetic part (prepares for emergency: "fight or flight", faster heart) and the parasympathetic part (calms the body, restores normal).

Brain. It weighs about 1.4 kg in an adult and sits in the skull (cranium). It is covered by three membranes (meninges) and cushioned by cerebrospinal fluid.

The cerebrum has two halves (hemispheres) with a wrinkled surface that raises its area. The grey matter is outside the cerebrum; the spinal cord has white matter outside and grey matter inside.

Spinal cord. It runs inside the vertebral column (backbone) and carries messages to and from the brain. It controls reflex actions.

Reflex action. An automatic, quick, involuntary response to a stimulus without thinking. Examples: pulling the hand away from a hot object, blinking, coughing, knee jerk, salivation at the smell of food. The path is called the reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector. The brain is told later. Reflexes protect the body from harm. Sneezing and vomiting are controlled by the medulla.

Voluntary and involuntary actions. Voluntary actions are done by will and controlled by the cerebrum (writing, walking). Involuntary actions work without will (heartbeat, digestion) and are controlled mainly by the medulla.

Sense organs

Humans have five sense organs: eye (sight), ear (hearing and balance), nose (smell), tongue (taste) and skin (touch, pressure, heat, cold, pain).

Eye. The outer white layer is the sclera, with the transparent cornea at the front. The iris is the coloured part with an opening, the pupil, which controls the light entering; in bright light the pupil becomes small. The lens focuses light on the retina at the back. The retina has rod cells (dim light vision) and cone cells (bright light and colour). The optic nerve takes the impulse to the brain. The yellow spot (fovea) has the sharpest vision; the blind spot has no cells for light. Rhodopsin is made from vitamin A. The lens is adjusted by ciliary muscles (accommodation). Defects: myopia (short-sight, corrected by a concave lens), hypermetropia (long-sight, convex lens), cataract (cloudy lens, treated by surgery), colour blindness.

Ear. It has the outer ear (pinna and canal), the middle ear (tympanic membrane or eardrum and three small bones: malleus, incus and stapes) and the inner ear (cochlea for hearing and semicircular canals for balance). The Eustachian tube links the middle ear to the throat.

Tongue and nose. Taste buds on the tongue sense sweet, sour, salty, bitter and umami. The nose has olfactory cells for smell.

Endocrine coordination (brief)

Hormones are chemical messengers made by endocrine glands and carried by blood. Pituitary is the master gland. Thyroid makes thyroxine; pancreas makes insulin; adrenal makes adrenaline (emergency hormone); testis makes testosterone; ovary makes oestrogen. Insulin lack causes diabetes; thyroxine needs iodine.

Plant coordination

Plants have no nerves. They respond slowly with growth movements controlled by hormones.

Tropism is the growth movement of a plant part in response to a stimulus. It is positive if towards the stimulus and negative if away.

Nastic movements do not depend on the direction of the stimulus: the leaves of touch-me-not (Mimosa pudica) fold on touch. Such quick movement is due to loss of water pressure in cells. Leaves of some plants close at night (sleep movement).

Plant hormones (phytohormones).

Charles Darwin and his son first studied bending of canary grass seedlings towards light; F. W. Went later worked on it in oat seedlings. Auxin collects on the shaded side and makes that side grow faster, so the shoot bends towards light. Apical dominance means the terminal bud stops the side buds from growing; cutting the tip makes the plant bushy. Fruit-growers use ethylene (as ethephon) for ripening of banana and mango, and auxin for seedless fruits.

Teaching angle

Use reaction-time games (catching a dropped ruler), blinking and pupil change activities, and growing seedlings in a box with a light hole to show phototropism. Use simple charts for the reflex arc and avoid confusing learners by mixing too many terms in one lesson. Ask learners to give an example from daily life for each response.

Exam traps

• Cerebrum is for thinking; cerebellum is for balance; medulla is for involuntary actions.
• The reflex action is controlled by the spinal cord, not the brain.
• Auxin promotes growth; abscisic acid inhibits growth.
• Gibberellin elongates the stem; cytokinin promotes cell division.
• Ethylene is the only gaseous plant hormone.
• Rods are for dim light; cones for colour and bright light.
• Myopia uses a concave lens; hypermetropia uses a convex lens.
• Sensory neurons bring impulses in; motor neurons carry impulses out.

One-liners

• 1. The neuron is the unit of the nervous system.
• 2. The axon carries the impulse away from the cell body.
• 3. The synapse is the gap between two neurons.
• 4. The cerebrum is the largest part of the brain.
• 5. The cerebellum maintains balance.
• 6. The medulla controls breathing and heartbeat.
• 7. The spinal cord controls reflex actions.
• 8. Pituitary is called the master gland.
• 9. Adrenaline is the emergency hormone.
• 10. Auxin makes the shoot bend towards light.
• 11. Ethylene ripens fruits.
• 12. Touch-me-not leaves fold when touched.

Practice questions

1. The structural and functional unit of the nervous system is the

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

   A. neuron

   The neuron is the nerve cell.

2. Which part of a neuron carries the impulse away from the cell body?

   1. Dendrite
   2. Axon
   3. Nucleus
   4. Synapse
   Answer

   B. Axon

   Dendrites receive; the axon sends.

3. The largest part of the human brain is the

   1. medulla
   2. hypothalamus
   3. cerebrum
   4. cerebellum
   Answer

   C. cerebrum

   Cerebrum forms most of the brain.

4. Balance of the body is maintained by the

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

   D. cerebellum

   Cerebellum coordinates movement and posture.

5. Heartbeat and breathing are controlled by the

   1. cerebrum
   2. pituitary
   3. medulla oblongata
   4. cerebellum
   Answer

   C. medulla oblongata

   Medulla controls involuntary actions.

6. A reflex action is controlled mainly by the

   1. cerebellum
   2. cerebrum
   3. hypothalamus
   4. spinal cord
   Answer

   D. spinal cord

   Reflex arc passes through the spinal cord.

7. The gap between two neurons is called a

   1. synapse
   2. dendron
   3. axon
   4. myelin sheath
   Answer

   A. synapse

   Neurotransmitters cross the synapse.

8. The plant hormone that ripens fruits is

   1. cytokinin
   2. ethylene
   3. auxin
   4. gibberellin
   Answer

   B. ethylene

   Ethylene is a gas that ripens fruits.

9. Bending of a shoot towards light is called

   1. thigmotropism
   2. phototropism
   3. geotropism
   4. hydrotropism
   Answer

   B. phototropism

   Photo means light.

10. Which plant hormone promotes cell division?

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

    C. Cytokinin

    Cytokinin promotes division.

11. Which plant hormone promotes stem elongation and seed germination?

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

    A. Gibberellin

    Gibberellins make stems longer.

12. The growth inhibitor hormone that also closes stomata in drought is

    1. auxin
    2. gibberellin
    3. cytokinin
    4. abscisic acid
    Answer

    D. abscisic acid

    ABA is a stress hormone.

13. Coiling of tendrils around a support is an example of

    1. thigmotropism
    2. chemotropism
    3. geotropism
    4. phototropism
    Answer

    A. thigmotropism

    Thigmo means touch.

14. Folding of leaves of the touch-me-not plant on touching is an example of

    1. phototropism
    2. geotropism
    3. hydrotropism
    4. nastic movement
    Answer

    D. nastic movement

    The response is not directed towards the stimulus.

15. Root growing downward into soil shows

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

    C. positive geotropism

    Roots respond towards gravity.

16. Which cells of the retina work in dim light?

    1. Fovea cells
    2. Rods
    3. Cornea cells
    4. Cones
    Answer

    B. Rods

    Rods are for dim light; cones are for colour.

17. Which defect of the eye is corrected by a concave lens?

    1. Cataract
    2. Hypermetropia
    3. Myopia
    4. Colour blindness
    Answer

    C. Myopia

    Short-sight needs a diverging lens.

18. The part of the eye that controls the amount of light entering is the

    1. cornea
    2. retina
    3. sclera
    4. iris
    Answer

    D. iris

    Iris changes the pupil size.

19. Which of the following is the master gland of the body?

    1. Pituitary
    2. Adrenal
    3. Pancreas
    4. Thyroid
    Answer

    A. Pituitary

    Pituitary controls many other glands.

20. Number of pairs of cranial nerves in humans is

    1. 10
    2. 12
    3. 24
    4. 31
    Answer

    B. 12

    Humans have 12 pairs of cranial nerves.

21. Number of pairs of spinal nerves in humans is

    1. 46
    2. 31
    3. 24
    4. 12
    Answer

    B. 31

    There are 31 pairs.

22. The three small bones in the human middle ear are the

    1. malleus, incus and stapes
    2. pinna, incus and stapes
    3. cochlea, malleus and incus
    4. stapes, cochlea and canal
    Answer

    A. malleus, incus and stapes

    They pass sound to the inner ear.

23. The part of the ear that helps in balance is the

    1. pinna
    2. cochlea
    3. Eustachian tube
    4. semicircular canals
    Answer

    D. semicircular canals

    Semicircular canals sense balance.

24. The path of a reflex arc is

    1. receptor → motor neuron → brain → sensory neuron → effector
    2. effector → spinal cord → sensory neuron → receptor
    3. receptor → brain → effector only
    4. receptor → sensory neuron → spinal cord → motor neuron → effector
    Answer

    D. receptor → sensory neuron → spinal cord → motor neuron → effector

    Sensory goes in, motor goes out.

25. A student touches a hot vessel and withdraws her hand before feeling the heat. This is an example of

    1. a voluntary action
    2. a plant movement
    3. a reflex action
    4. a hormone action
    Answer

    C. a reflex action

    Quick, automatic response via the spinal cord.

26. A brain part that links the nervous and endocrine systems and controls body temperature is the

    1. cerebrum
    2. hypothalamus
    3. cerebellum
    4. medulla
    Answer

    B. hypothalamus

    Hypothalamus regulates temperature, hunger and thirst.

27. Which of the following is the emergency hormone secreted by the adrenal gland?

    1. Adrenaline
    2. Thyroxine
    3. Insulin
    4. Oestrogen
    Answer

    A. Adrenaline

    Adrenaline prepares the body for fight or flight.

28. A reaction-time activity in which a student catches a dropped ruler is best used in class to show

    1. the structure of a cell
    2. how plants grow
    3. the time taken for a nerve response
    4. food tests
    Answer

    C. the time taken for a nerve response

    It links stimulus and response.

29. To demonstrate phototropism in class, the most suitable set up is

    1. seedlings kept in salt water
    2. seedlings kept in complete darkness
    3. seedlings in a box with a hole for light on one side
    4. seedlings with a fan on
    Answer

    C. seedlings in a box with a hole for light on one side

    Shoots bend towards the light hole.

30. Removal of the tip of a plant makes it bushy because

    1. leaves become auxin
    2. the side buds are freed from apical dominance
    3. roots stop growing
    4. flowers turn into fruit
    Answer

    B. the side buds are freed from apical dominance

    The terminal bud's auxin inhibits side buds.

31. Consider the statements. 1. Sensory neurons carry impulses to the brain or spinal cord. 2. Motor neurons carry impulses to muscles. 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 correct.

32. Consider the statements. 1. Cerebellum controls thinking and memory. 2. Medulla controls vomiting and sneezing. Which is/are correct?

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

    B. 2 only

    Thinking is by the cerebrum.

33. Consider the statements. 1. Auxin helps shoot bending towards light. 2. Ethylene is a growth-promoting liquid hormone. Which is/are correct?

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

    A. 1 only

    Ethylene is a gas.

34. Consider the statements. 1. Cones work in bright light. 2. Rods help in colour vision. Which is/are correct?

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

    A. 1 only

    Colour vision is by cones.

35. Consider the statements. 1. Plants have a nervous system. 2. Plant coordination is through hormones. Which is/are correct?

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

    B. 2 only

    Plants have no nerves.

36. Consider the statements. 1. Abscisic acid inhibits growth. 2. Gibberellin breaks seed dormancy. 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 correct.

37. Consider the statements. 1. The sympathetic system prepares the body for emergency. 2. The parasympathetic system makes the heart beat faster. Which is/are correct?

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

    A. 1 only

    The parasympathetic system calms the body.

38. Consider the statements. 1. The spinal cord has grey matter inside. 2. The spinal cord is protected by the vertebral column. 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 correct.

39. Match the tropism with its stimulus. (a) Geotropism (b) Hydrotropism (c) Chemotropism (d) Thigmotropism (p) Touch (q) Water (r) Gravity (s) Chemicals

    1. a-r, b-q, c-p, d-s
    2. a-r, b-s, c-q, d-p
    3. a-q, b-r, c-s, d-p
    4. a-r, b-q, c-s, d-p
    Answer

    D. a-r, b-q, c-s, d-p

    Gravity, water, chemicals and touch.

40. Match the brain part with its function. (a) Cerebrum (b) Cerebellum (c) Medulla (d) Hypothalamus (p) Balance (q) Thinking (r) Breathing control (s) Body temperature

    1. a-s, b-p, c-r, d-q
    2. a-q, b-r, c-p, d-s
    3. a-p, b-q, c-r, d-s
    4. a-q, b-p, c-r, d-s
    Answer

    D. a-q, b-p, c-r, d-s

    Standard brain functions.

41. Match the hormone with its plant effect. (a) Auxin (b) Gibberellin (c) Cytokinin (d) Ethylene (p) Fruit ripening (q) Cell elongation (r) Stem growth (s) Cell division

    1. a-q, b-r, c-p, d-s
    2. a-q, b-s, c-r, d-p
    3. a-r, b-q, c-s, d-p
    4. a-q, b-r, c-s, d-p
    Answer

    D. a-q, b-r, c-s, d-p

    Auxin elongates cells; gibberellin stem growth; cytokinin division; ethylene ripening.

42. Arrange the path of light in the eye.

    1. Pupil, cornea, lens, retina
    2. Retina, lens, pupil, cornea
    3. Cornea, lens, pupil, retina
    4. Cornea, pupil, lens, retina
    Answer

    D. Cornea, pupil, lens, retina

    Light enters through the cornea, pupil, lens to the retina.

43. Defect in the eye in which the lens becomes cloudy is

    1. hypermetropia
    2. cataract
    3. myopia
    4. colour blindness
    Answer

    B. cataract

    Surgery replaces the cloudy lens.

44. Which vitamin is needed to form the pigment in rod cells?

    1. Vitamin A
    2. Vitamin K
    3. Vitamin C
    4. Vitamin D
    Answer

    A. Vitamin A

    Vitamin A is used to make rhodopsin.

45. A plant tendril coils around a stick. This movement is controlled by

    1. muscles
    2. kidneys
    3. nerves
    4. plant hormones
    Answer

    D. plant hormones

    Plants lack nerves and muscles.