Monday, April 6, 2020






  1. O’ Level Study Notes All Subjects
  2. A’ Level Study Notes All Subjects
  3. Pats Papers


In this topic you will learn about concept of coordination, nervous coordination inhumans, sense organs, drugs and drug abuse in relation to nervous coordination, andcoordination in plants.
Coordination is the working together of the various organs of an organism in a systematic manner so as to produce a proper response to the stimuli. Without coordination the body becomes disorderly and it may fail to function properly.

The Ways in Which Coordination is Brought About
The coordination in simple multicellular animals takes place through nervous systemonly. The control and coordination in higher animals called vertebrates (including humanbeings) takes place through nervous system as well as hormonal system called endocrinesystem. Coordination in plants is under the control of hormones.
All the living organisms (plants and animals) respond and react to changes in the environment around them. The changes in the environment to which the organisms respond and react are called stimuli (singular: stimulus). The living organisms show response to stimuli such as light, heat, cold, sound, smell, taste, touch, pressure, pain,water, and force of gravity, etc. The ability to perceive, interpret and respond to stimuli is called irritability or sensitivity.
There are two types of stimuli:
  • external
  • internal.

External stimuli are associated with the surrounding environment such as wind temperature, light, pressure, touch, water and gravity.

Internal stimuli occur within the organism, for example, a decrease or an increase in the amount of water and glucose in the blood.

When an organism detects a stimulus, it initiates a response. A response is a behavioural,physiological or muscular activity initiated by a stimulus. For example, if a man touches a very hot utensil accidentally, he quickly pulls his hand away from the hot utensil. Here,heat is the stimulus and the man reacts (responds) by moving his hand away from the hot utensil. Similarly, when the sun is bright, we close our eyes. In this case, light is the stimulus and we react by closing our eyes. Likewise, when the amount of water in the blood drops, the pituitary gland secretes an anti-diuretic hormone (ADH) which stimulates the reabsorption of water in the kidneys.
Multicellular organisms detect stimuli through sense organs called receptors. A receptor is a sense organ (e.g. eye) or sensory nerve ending (e.g. in the skin or internal organ) which receives stimuli and sets nervous impulses. Impulses are electrical transmissions or chemical stimuli that are sent from the receptor to the coordinating system in the organism. The organs that respond to the stimuli are called effectors. A coordinator is an organ (e.g. the brain and spinal cord) that receives messages from the receptors,translates them and sends the information back to an effector for action. An effector is a muscle or gland which receives impulses from nerves, brain or spinal cord and responds to them. Response is the end-action, such as a muscle contracting to cause the movement of the arm. The diagram below illustrates the five components of coordination in mammals.


Coordination in Plant, Concept of Tropic and Nastic Responses
The Concept of Tropic and Nastic Responses
Explain the concept of tropic and nastic responses
Both, plants and animals react (or respond) to various stimuli around them. But themethod of reacting to stimuli is not similar in plants and animals. They react to stimuli indifferent ways. For example, plants bend towards light but animals do not bend towardslight. The animal amoeba reacts to the presence of food by moving towards the foodparticle.
The plants do not have a nervous system and sense organs like eyes, ears, or nose, etc.,like the animals, but they can still sense things. The plants can sense the presence ofstimuli like light, gravity, chemicals, water, and touch, etc., and respond to them. Theysense these stimuli by using hormones in them.

The stimuli like light, gravity, chemicals, water, and touch, etc., are called environmental changes. So, we can also say that the plants coordinate their behaviour against environmental changes by using hormones. The hormones in plants do not act the sameway as in animals.
The hormones in plants coordinate their behaviour by affecting the growth of a plant.And the effect on growth of the plant can result in the movement of a part of the plantlike shoot (stem) or root, etc towards a certain stimulus.
Experiments to Investigate the Effects of Tropic and Nastic Responses in Plants
Carry out experiments to investigate the effects of tropic and nastic responses in plants
Plants receive and respond to a variety of stimuli that are important to their survival in the environment. These responses allow the plants to survive, grow, develop and reproduce.The movement of plants in the direction of stimulus is known as ‘tropism’. Tropisms aregrowth responses of plants that result in curvatures of plant organs toward or away fromcertain stimuli. Tropisms can be positive, in which case the plant will bend toward astimulus, or negative, in which case the plant will bend away from a stimulus.
The other movements shown by the plants are associated with the growth of the plants.For example, the shoot system moves towards sunlight and the root system towards earth.Thus, the plants also respond to their environment.
Important tropisms in plants include phototropism, geotropism, hydro tropism,chemo tropism and thigmotropism.
Phototropism is the tendency for plant organs to bend in response to a directional light source. For example, light streaming in a window from one direction will often cause the stems of plants placed nearby to bend toward the window, a positive phototropism.
Most plant shoots are positively phototropic because they tend to grow towards light.Most roots are negatively phototropic because they away from light.

The Importance of Tropic and Nastic Responses
Importance of phototropism
Phototropism is important to plants because of it enables the plant leaves to be placed under direct sunlight to absorb maximum light so as to carry out photosynthesiseffectively.
Geotropism is the movement of a part of the plant towards gravity. In most plants, roots-grow downward with gravity while shoots grow upward against gravity. Within hours,the shoot of a plant placed on its side will usually bend upward and the roots will benddownward as the plant reorients its direction of growth in response to gravity.
Most plant roots grow towards gravity and are said to be positively geotropic. Mostshoots grow away from gravity and are said be negatively geotropic.
Importance of geotropism
Geotropisms are important to plants because of the following reasons:
  1. It enables the plants to send roots into the ground hence anchoring the plant firmlyinto the soil.
  2. It enables plant roots to absorb water and mineral salts from the soil.
  3. Negative geotropism exhibited by the shoot enables the shoot to grow upwards, and in so doing, exposes the plant leaves to maximum sunlight for effective photosynthesis
Hydrotropism is the movement of a plant or part of a plant towards water. Plant roots normally grow towards moisture. They are therefore positively hydrotropic. If you plant a plant near a water source such as porous pot or river, the roots will always grow towardswater.
Importance of hydrotropism
It enables the plants to absorb dissolved minerals and water. Water is necessary forvarious functions such as:
  1. Photosynthesis
  2. Numerous physiological reactions that take place within plant cells.
  3. Turgor pressure, which aids in plant support.
  4. Dissolution of mineral salts.

An example of positive and negative chemo-tropism is shown by a plant‘s roots; the roots grow towards useful minerals displaying positive chemo-tropism, and grow away fromharmful acids displaying negative chemo-tropism.
Chemotropism is the movement or growth of an organism or part of an organism in response to a chemical stimulus. During the process of fertilization the movement of pollen tube towards ovule due to secretion of a sugary chemical in the ovary is an example of chemotropism
Importance of chemotropism
  1. It enables the plant to absorb mineral salts from the soil when the roots grow towards beneficial chemicals such as fertilizers.
  2. Negative geotropism, such as when plant roots grow away from the toxins, enables the plant to survive by avoiding contact with such harmful chemicals.
  3. . It facilitates the fertilization process in flowering plants.
Thigmotropism or haptotropism
Thigmotropsim refers to non-directional movements which take place neither towards noraway from the stimulus. The best example of nastic movement is folding and drooping ofleaves of Mimosa pudica plant when its leaves are touched with fingers or any object.The leaves fold even when swayed about by wind. Also the specialized touch-sensitivetendrils of many vining plants, such as pea, will bend toward the side receiving a touchstimulus. Continual stimulation can lead to the coiling of the tendril around an object,which enables vining plants to grasp objects on which they can climb
Importance of thigmotropism
  1. Thigmotropism enables crawling plants to climb up higher plants and expose their leaves to sunlight for optimum photosynthesis.
  2. It enables the insectivorous plants such as the Venus flytrap to trap insects and digestthem to obtain nutrients.


4/ 5

No comments: