control and coordination

stimuli

stimuli

the changes in the environment to which the organisms respond and react to are called stimuli. the organisms usually react in the form of movement

eg: light, heat, cold, sound, smell

difference in response to stimuli between animals and plants

animals can react to stimuli in many different ways as they have a nervous and endocrine system while the plants react to stimuli in limited ways as they dont have a nervous system and can only use hormones to create a response

definition of coordination and why its necessary

the working together of various organs of an organism in a systematic manner so as to produce a proper response to stimulus is called coordination

this is because various organs are involved in order to respond in a manner which is in the best interest of our body

control and coordination in plants

plants can sense the presence of stimuli like light, gravity, chemicals etc. and react to it by the action of hormones in them. hence we can say that plants coordinate their behaviour against environmental changes by using hormones

because they have no nervous system and only depend on hormones, the response to stimuli is very slow

the hormones in plants coordinate their behaviour by affecting the growth of the plant in required areas

phytohormones (plant hormones)

there are four main types of phytohormones;

auxin: promotes cell enlargement and differentiation. synthesised in the tip of root and shoot. controls plants response to gravity and light

gibberellin: helps in growth of stem and flowers, germination of seeds

cytokinin: promotes cell division, delays plant/leaf aging, stimulates leaf expansion

abscisic acid: reverses growth promoting effects of auxin & gibberellin

ethylene: promotes transverse growth, ripening of fruit

how plant hormones cause movement in plants

the movements of the plant parts are caused by unequal growth in two regions by the action of plant hormones

for example; if one side of a stem has more auxin than the other side, that side will grow faster causing the stem to bend

tropisms (tropic movements)

a growth movement of a plant part in response to stimulus in which the direction of the stimulus determines the direction of the response is called tropism. thus, tropism is a directional movement

the growth/movement of the plant part towards the stimulus is called positive tropism

the growth/movement of the plant part away from the stimulus is called negative tropism

phototropism

the movement of a plant part in response to light is called phototropism. the movement towards light is said to be positive while the movement away from light is said to be negative. this is due to the action of auxin hormone

the movement of stem towards light is said to be positive phototropism while the movement of roots away from light is said to be negative phototropism

geotropism

the movement of a plant in response to gravity is called geotropism. the movement towards the pull of gravity is said to be positive while the movement away from the pull of gravity is said to be negative

the movement of roots towards the pull of gravity is called positive geotropism while the movement of stem away from the pull of gravity (to ensure that they get light) is called negative geotropism

chemotropism

the movement of a plant part in response to chemicals is called chemotropism

the growth of pollen tube towards the ovule is the result of chemotropism

hydrotropism

the movement of a part plant towards water is called hydrotropism

the roots of the plants always move towards the water even if it means its going against the pull of gravity

thigmotropism

the movement of a part plant towards touch is called thigmotropism

the coiling of tendrils (thread-like growth on climbing plants which are sensitive to touch) is due to thigmotropism

use of tropic movements

the various tropic movements help the plants to survive. they help plants to obtain water, nutrients and light which are necessary for their growth and survival

nasties (nastic movements)

the movement of a plant part in response to stimulus in which the direction of the response is NOT determined by the direction of the stimulus is called nastic movement. it is also called non-directional movement

thigmonasty: non-directional movement of a plant part in response to touch. example: leaves of mimosa pudica (touch-me-not plant). this response is caused by the sudden loss of water in the leaves

photonasty: non-directional movement of a plant part in response to light. example: opening and closing of flowers in response to light

systems involved in control and coordination in humans

the control and coordination in humans takes place through nervous system as well as hormonal system called endocrine system

classification of nervous system

the nervous system can be divided into two parts;

central nervous system: consisting of brain and spinal cord

peripheral nervous system: consisting of all nerves

receptors

a receptor is a cell in a sense organ which is sensitive to a particular type of stimulus. these receptors receive stimuli from the environment and send the message through the sensory nerves in the form of electrical impulses

eg: photoreceptors in eyes detect light, phonoreceptors in ears detect sound, olfactory receptors in nose detect smell, gustatory receptors in tongue detect taste

functions of the nervous system

coordinates the activities in our body and helps all systems of our body to work together

coordinates involuntary actions like heartbeat and breathing

receives information, processes it, interprets it and responds accordingly

structure and function of neuron

the nervous system is made up of units called nerve cells or neurons. they are the largest cells in our body. it has three components;

cell body: a typical cell which contains cytoplasm and nucleus

dendrites: thin fibres on the cell body. pick up electrical impulses

axon: longest fibre on the cell body. has a protective covering made up of myelin. passes electrical impulses through nerve endings

how electrical impulses are transferred from one neuron to another

the electrical impulses are transferred from one neuron to another through a microscopic gap between the two neurons called synapse

the nerve ending of one neuron releases some chemical substance into the synapse which then creates a similar electrical impulse in the dendrite of the next neuron. this process continues until the impulse reaches its destination. synapses ensure that the impulses are unidirectional

types of neurons in nervous system

sensory neurons: transmit impulses from receptors towards the CNS

motor neurons: transmit impulses from the CNS to the muscle cells (effectors)

relay neurons: occur in the CNS where they serve as links between the sensory and motor neurons

cranial neurons: connect parts in the head to the brain

spinal neurons: connect rest of the body parts to the spinal cord

reflex action

it is a quick, automatic involuntary action in response to stimuli. it is performed automatically without our awareness. it involves the brain only if the receptor and effector is in the head. otherwise, it mostly involves the spinal cord

ex: touching a hot vessel, contraction of pupil in the presence of bright light

reflex arc

the pathway taken by the nerve impulses in a reflex action is called the reflex arc

stimulus → receptor → sensory nerve → spinal cord/brain (relay nerve) → motor nerve → effector → response

how effectors cause action/movement

muscles are made up of muscle cells, which contain special proteins. when stimulated by electrical impulses, a rearrangement of these proteins takes place causing the muscle cells to change shape and contract

central nervous system

CNS consists of the brain and spinal cord. its role is to direct incoming messages to the motor neurons that are connected to the part of the body which will respond to the stimulus. in complicated responses, both brain and spinal cord are involved

the job of the CNS is to collect all the information from all receptors, which is added together before messages are sent out to the effectors

exterior structure of brain

the brain is located inside the skull of the body at the top of the spinal cord

it is protected by a bony box called cranium

it is surrounded by membranes. the spaces between the membranes is filled with cerebro spinal fluid which protects the brain from shocks

interior structure of the brain

• forebrain

  • cerebrum: thinking part of the brain. controls voluntary actions. stores information

  • hypothalamus: responsible for hormone production

  • olfactory lobes: process information about smell

• midbrain: connects forebrain and hindbrain. controls reflex movements of the head and neck

• hindbrain

  • pons: regulate respiration and controls sleep cycle

  • cerebellum: helps in maintaining posture and balance

  • medulla: controls involuntary actions like breathing, blood pressure, heart beat etc.

definition of hormone

the chemical substances which coordinate the activities and growth of living organisms are called hormones

glands and its types

a gland is a structure which secretes a specific substance into the body. it is of two types;

exocrine gland: excretes its products into a duct. example: salivary gland excretes saliva into the salivary duct

endocrine gland: excretes its products directly into the blood. it is also called a ductless gland. examples: hormone secretion

some glands are both exocrine and endocrine. for example, pancreas acts as an endocrine gland and secretes insulin. it also acts as an exocrine gland by secreting enzymes into the pancreatic duct

hypothalamus

it is an endocrine gland present in the brain. it regulates hormone secretions in the pituitary gland

pituitary gland

it is an endocrine gland present right below the brain. it secretes several hormones such as growth hormone which controls the development of bones and muscles

thyroid gland

it is an endocrine gland attached to the wind pipe. it makes a hormone called thyroxine which contains iodine. its function is to control the rate of metabolism.

iodine is necessary for the making of thyroxine hormone. a deficiency of iodine can result in a deficiency of thyroxine, which in turn results in a disease called goitre

pancreas (endocrine)

it is located just below the stomach. it secretes the hormone called insulin. the function of insulin is to lower blood sugar level. deficiency of insulin is called diabetes, which results in high sugar levels

adrenal glands

there are two adrenal glands which are located on the top of two kidneys. they secrete the adrenaline hormone, which regulates heart rate and blood pressure. it also helps the body to adjust in the case of an emergency

testes

they are glands which are only present in males. they make the male sex hormones called testosterone, which helps in release of male gametes and development of secondary sexual characters

ovaries

they are glands that are only present in females. they secrete the female sex hormones called estrogen, which helps in the release of female gametes and development of secondary sexual characters

limitations of the nervous system

electrical impulses reach the cells which they are connected to only, but not each and every cell

cells cannot continuously create and transmit impulses. once an impulse is generated in a cell and transmitted, the cell will take some to reset its mechanism before it can generate new impulse