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Root pressure, Transpiration, Nerve cell, Human brain, Reflex action

Root pressure: After absorbing water from the soil root cell swells (turgid). The turgid root cell put pressure on the adjacent root cell. This pressure is called root pressure. Water and minerals reach to the water conducting (xylem) of the root due to this pressure.

Transpiration: Removal of water in the form of vapours through pores (stomata) present in the leaves is called transpiration. It occurs during day. Transpiration promotes absorption and distribution of water and minerals. It gives cooling effect to the plants.

Nerve cell: Nerve cell or neuron is the largest cell of the human body. It consist of a cell body, dendrites and axon. Neurons are the structural and functional units of the nervous system. They conduct impulses from one place to another in the body.

Human brain: Human brain is very delicate organ. An adult human brain weighs about 1.3 kg to 1.4 kg and has 100 billion of nerve cells. It is the main controlling part of the nervous system and it is safely located in the cranial cavity. It is protected by three layers called meninges. In the brain there are various cavities called ventricles. In the ventricles the long tubular cavity of the spinal cord is called the ‘central canal’. The ventricles, central canal and in the layers of meninges are filled with cerebro-spinal fluid. This fluid supplies nutrients to the central nervous system and protects it from shock.

The human brain has the following parts:

i. Cerebrum: The largest part of the brain, occupies two-thirds of brain and consists of two cerebral hemispheres. They are joined by nerve tracts. It control of voluntary movements such as decision-making, memory, intelligence.

ii. Cerebellum: this part is smaller than the cerebrum, situated below the cerebrum at the back of the cranial cavity. It maintains the body’s balance and co-ordinates of voluntary movements.

iii. Medulla oblongata: The hind-most part of brain. The medulla oblongata continues downwards as the spinal cord. It controls involuntary activities (activities which are not our control) such as of the heart, blood circulation, breathing, sneezing, coughing, etc.

Reflex action: Reflex actions are sudden, automatic reactions of the body in response to stimuli (The change which promotes a reaction in an organ or tissue in response to that change). Reflex actions occur without the involvement of the brain, these actions involved spinal cord.

For examples, contraction of the pupils of the eye when exposed to light, Withdrawal of the hands when one touches a burning candle.