Standard 10 The Regulators of Life

Gurudatta K Wagh

Control Systematic regulation of various activities

Co-ordination Orderly execution of the activities

Co-ordination is necessary between organs and

organ systems that bring about all the inter-related life

processes

Homoeostasis Maintenance of the steady state by

different systems of an organism for its optimal

functioning because of perfect co-ordination

Co-ordination in plantsPlants do not have a nervous system or muscular systemThe movements exhibited by plants are mainly in response to the stimulus

A seedling and its movement•The movement of a seedling is because of growth•If growth is prevented, it (seedling) does not exhibit any movement

Seismonastic movement (stimulus of touch) Mimosa

When tendrils come in contact with any object, the portion of the tendril which is in contact with the object grows slowly and the other portion grows fast and entwines around the object

Tendrils are sensitive to touch

Plants exhibit two types of movements, 1) growth dependent, and 2) growth independent

1) Growth Dependent Movement

Tropism or tropic movement The movement or growth of any part of a plant in response to an external stimulus

Phototropic movement (Phototropism) The shoot of any plant grows in the direction of source of light When a potted plant is kept near the window in a room the stem bends slightly towards the window

Shoot When light falls on a part of the plant, a hormone called auxin which is synthesized at the tip of the shoot helps the cells to grow longer

As the light is falling on one side of the plant, the

hormone auxin diffuses towards the side of the shoot

which is not in sunlight and stimulates the cells to

grow longer Hence the plant appears to bend towards light

Gravitropic and hydrotropic movements

Root The root system of the plants responds to the

stimulus of gravity and water

The growth of pollen

tubes towards the

ovules in response

to certain chemicals

Chemotropic movement (Chemotropism)

Examples of plant hormones

Auxins, Gibberellins - growth of the stem

Cytokinins - promote cell division; fruits, seeds

Abscissic acid - inhibits growth and leads to wilting of

leaves

2) Growth Independent Movement

Hormones bring about various movements in plants in response to the changes occurring in the surroundings

Plants use electrochemical means to transfer information from one cell to another as there is no specialized tissue present for the conduction of information Movement is also brought about as the plant cells change their shapes by altering the amount of water in them. The cells either swell or shrink and thus change their shapes

•The Venus flytrap has a trap which looks and smells like a flower to insects. When insects land on it, they touch a trigger hair which slams the trap shut and they are then digested by the plant

•Lotus opens in the morning and the tuberose at night

•The tentacles on the leaves of the insectivorous plants like drosera curl inwards at the touch of an insect and trap the insect

•The explosive fruit of balsam plant bursts open at an appropriate time and scatters the seeds

Co-ordination in human beingsIn human beings the co-ordination of different bodily activities are controlled by (1) nervous control and (2) chemical control. The components of the human nervous system are the brain, spinal cord and the nerves.

11.3.1 The human nervous system The nervous system can be divided into (i) the central nervous system (CNS), (ii) the peripheral nervous system (PNS) and (iii) the autonomic nervous system (ANS)

(i) Central nervous system (CNS) Comprises of the brain and the spinal cord and regulates all activities of the body

(ii) Peripheral nervous system (PNS) Includes all the nerves. The nerves form a network and spread throughout the body and connect all parts of the body to the CNS (iii) Autonomic nervous system (ANS) Comprises of all the nerves present in the involuntary organs like heart, stomach, lungs, etc.

Nerves(i) Afferent nerves carry impulses from the sensory organs to the brain

(ii) Efferent nerves carry impulses from the brain to the sensory organs

Structure The nerves are composed of neurons and neuroglia. The neurons are specialized cells capable of creating and transmitting electrochemical impulses. The neuroglia are supportive cells which assist the neurons in their function

Specialized tips of dendrites of a neuron pick up the information from our environment. It sets off a chemical reaction producing an electrical impulse which travels from the dendrite to the cell body and from there, through the axon (nerve fibre) to its end

Journey of an impulse

At the end of the first axon, the electrical impulse induces the release of some chemicals

These chemicals go across the small gap (synapse) of 2- 20 nanometre (nm) between the neurons and start a similar electrical impulse in the dendrite of the next neuron

This is the procedure by means of which the impulses travel in the body from the neurons and are delivered to the muscle cells or glands

Journey of an impulse

The movement at the cellular level takes place when the cells change their shape, so that they shorten. Muscle cells possess special kinds of proteins which are capable of bringing about change in their shape and make the cell capable to respond to the nervous electrical impulses.

Muscle tissue When an action or movement has to be brought about, the muscle tissue does the final job. The muscle cells should move to enable work to be done.

Nervous tissue is composed of a highly organized network of neurons capable of transferring information in the form of electrical impulses from one part of the body to another Classification of neurons

Sensory neurons conduct impulses from the sense organs to the brain and spinal cord

Motor neurons conduct impulses from the brain and spinal cord to the effector organs like muscles and glands

Association (Interneuron) neurons perform integrative functions of the nervous system

Types of neurons

For information

In unicellular amoeba there is no nervous system

The nervous system in hydra is at a very primitive stage

For information

A number of nerve cells come together and form a cluster in earthwormThese clusters are joined together to form a beaded structure called the nerve cord

Taste buds at the tip of the tongue detect sweet taste, those at the back – bitter taste, side – salty and sour

When we inhale smell enters the back of the nose . When we have a cold, food tastes odd because nasal organs get inflamed

Each side of our brain controls the opposite side of our body. Left – speaking, writing, logical thought. Right – artistic abilities

Sensory memory is weak

Short term memory lasts for 30 seconds

Long term memory retains things carefully learned and memorizedHormones (chemical messengers) are secreted by endocrine glands (glands of internal secretion)

Reflex Action Any sudden action in response to some happening in the environment

Nerves from all over the body meeting in a bundle is commonly called as the spinal cord. Reflex arcs are formed in the spinal cord.

In lower animals the complex neuron network needed for thinking is not there or is not well developed. Hence reflex arcs have been evolved as efficient ways of functioning in the absence of the true thought processes. In spite of the presence of complex neuron networks, reflex arcs continue to be more efficient for quick responses

The Central Nervous System (CNS)

•It is a delicate structure composed of the brain and

the spinal cord

•The brain is protected by a bony structure called the

cranium or skull and the spinal cord by the vertebral

column or the back bone

•Protective membranes called the meninges are

present in the space between the soft CNS and the

bone

•The ventricles, central canal and the space between

the meninges are filled with cerebrospinal fluid (CSF)

•CSF keeps the CNS well nourished and also

protects it by absorbing mechanical shocks.

•There are cavities present

on the different parts of the

brain known as ventricles

while the long cavity of the

spinal cord is called the

central canal

Many of our actions are voluntary in nature e.g. walking, clapping, bending, etc. In all these actions there is involvement of our muscles

The brain sends message to the muscles and the muscles act accordingly. This is the second instance where the nervous system is communicating with the muscles

Such a communication between the central nervous system and the other parts of the body is brought about by the Peripheral Nervous System (PNS) which is composed of cranial nerves arising from the brain and the spinal nerves arising from the spinal cord. The brain makes us think and we act based on our thinking

CNS and PNS

The brain is a complex organ divided mainly into three regions: 1) forebrain, 2) midbrain, 3) hindbrain Forebrain (cerebrum) Main thinking part of the brain. It has regions which receive the sensory impulses from various receptors Association centres The areas for smell, hearing, vision, etc. are separate. There are different areas where the sensory information received and interpreted are put together with the information received from other receptors as well as the information that is already stored in the brain. Such centres are known as association centres. On this basis a decision is taken on how to respond and the information is sent to the motor areas which control the movement of the voluntary muscles

Forebrain, midbrain, hindbrain

Midbrain and hindbrain Involuntary actions are controlled by the midbrain and hindbrain

Blood flow, breathing, sneezing, etc. are controlled by the medulla oblongata, a component of the hindbrain

Another component of the hind brain is cerebellum. It is responsible for coordinating the voluntary movements and also maintaining the balance of our body e.g. riding a bicycle, picking up an object from the floor, running along a straight line, etc.

The chemical control Hormones are secreted by the endocrine glands (ductless glands). These glands do not have any duct to transport their secretions. On production these hormones are directly released into the blood stream. Due to this, the hormones reach everywhere in the body, though the glands secreting them are located in particular places

Endocrine and nervous systems

Both the systems work in co-operation to integrate and control various body activities The significant difference between the two systems is that the nerve impulses (nervous system) are rapid and are usually of short duration while the hormonal action (endocrine system) is much slower and long lasting

It is very important that hormones should be secreted according to the requirement

When the sugar level of blood rises, it is detected by the cells of the pancreas which respond to the situation by producing more insulin. As the sugar level of the blood falls, the secretion of insulin is reduced

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