Science [2 Mark Questions]

→ Self-pollination : If the transfer of pollen occurs in the same flower from stamen to the stigma or it takes place between two different flowers of the same plant is called self-pollination.
→ Cross-pollination : If the pollen is transferred from one flower to another it is called cross-pollination.
→ This transfer of pollen from one flower to another is achieved by agents like wind, water or animals.

In sexual reproduction, both male and female reproductive cells arise from separate male and female parents. The traits of the parent with different traits are passed on to the offspring through sexual reproduction. Hence, generation to generation variation occurs. Species diversity arises due to continuous variations and sexual reproduction is also important for development. Some harmful recessive genes are not expressed.

If the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals it is known as regeneration.

Unicellular organism reproduce mostly through asexual mode of reproduction only some organism undergo sexual reproduction. Where as multicellular organism almost undergo sexual mode of reproduction.
In unicellular organism, asexual reproduction by the method of regenerative reproduction is not possible, whereas it is possible for simple multicellular organism.

Cell division in Amoeba can occur in any plane whereas is Leshmania, there is a whip - like structure at one end so binary fission occurs in a definite plane.

The variation found in different species give them the ability to survive in changing environment. If there is sudden change in the atmospheric conditions then some species might extinct. But some of them can live because of variation.
The one who lives can reproduce and produce new offsprings of there species and forms their new population. So we can say that variation is beneficial

→ First of all a small part is emerged from a parentcell. After that nucleus is then divided into two daughter cell. From that daughter nucleus is separated.
→ Gradually it separates from the parent cell as its reaches its proper size. See the figure.

• Cerebellum is the part of the brain that maintains posture and equilibrium of the body.

• The hormones are secreted from the endocrine glands which are ductless glands.
• These glands are richly supplied with blood.
• The secretions are directly poured in the blood stream.
• As the blood circulates in all the parts the body, these hormones are carried and hence present everywhere in the body.

• It is a reflex action-In this phenomenon, the impulse commencing from the sensory organ (the skin of the foot) enters into the spinal cord through the sensory nerve fibres.
• The impulse is analysed in the spinal cord and the responsive motor impulse is transmitted through the motor
• nerve fibres to the effector organ (the foot muscles) to contract and thereby show the response.
• So the foot is very suddenly lifted off as soon as it comes in contact with a burning coal.

• The central nervous system Comprises of a brain and a spinal cord.
• Brain is contained in a fluid-filled balloon which absorbs mechanical shocks and thereby protect it from any severe injuries.
• Moreover, the brain is enclosed in a strong bony box the cranium of the skull and the spinal cord is enclosed in
• a long and strong bony vertebral column.
• Thus, the central nervous system (of the human) is very well protected.

• The roots in plants show positive tropic movement in the direction of water and gravitational force, i.e., The roots show positive hydrotropism and positive geotropism.
• Thus, the roots bend in the direction of water and gravitational force.
• So it grows against the direction of light.

• Adrenaline prepares our body in an emergency situation.
• When adrenaline is secreted into the blood body shows following responses :
• The heart beats faster, breathing rate increases, blood pressure increases, skeletal muscles become more active, etc.
• This is known as fight or flight response.

• Auxins are growth promoting plant hormones that induce cell elongation.
• When tendril comes in contact with a support, auxin stimulates faster growth on to a part of tendril away from the support.
• This causes the tendril to coil around the support.

• Plant hormones are chemical compounds produced by plant itself and help to coordinate growth, development and responses to the environment.

• Olfactory receptors in our nose are stimulated by the smell of agarbatti.
• This causes generation of impulse which is received at dendrite of sensory neuron.
• Such impulse is transmitted to brain.
• In cerebrum message is interpreted and we detect the smell.

• Synapse is the gap between nerve endings of axon of one neuron and dendrites of another neuron.
• At the end of axon, the electrical impulse sets off the release of some chemicals.
• These chemicals cross the synapse and start a similar electrical impulse in a dendrite of the next neuron.

• Reflex action is an involuntary action controlled by spinal cord.
• Thinking is not involved in such action.
• Walking is a voluntary action and is controlled by a cerebellum, a part of hind-brain.
• This action is shown as per wish of an individual.

• A central nervous system is made-up of brain and spinal cord.
• Brain is a delicate organ and it is an important organ for a variety of activity, therefore, it needs to be carefully protected.
• Brain is protected in a bony box called cranium.
• Inside the bony box, the brain is covered by meninges.
• Fluid between the meninges protects brain by shock absorption.
• Spinal cord is protected in a hard skeletal structure called vertebral column or backbone.

• Reflex arcs have been evolved in animals because the thinking process of the brain is not fast enough.
• Many animals have very little or none of the complex neuron network needed for thinking.
• So it is quite likely that reflex arcs have evolved as efficient way of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

• Thinking is a complex activity and it is bound to involve a complicated interaction of many nerve impulses from many neurons.
• Thinking centres are located in fore-brain.
• It receives signals through nerves (Sensory) from various parts of the body.
• Thinking centres analyse the signals and prepare the instructions.
• From brain instructions are transmitted to effector organ through nerves (Motor).
• It takes more time to respond.
• In reflex action, instruction is generally given by spinal cord.
• So, the time to transmit impulse from organs to brain and from brain back to organ is saved in reflex action.
• That is why we give slow response when thinking is involved.

• There are touch (Thigmo) receptors in the skin.
• Skin is thus the sense organ.
• Touching a hot object may cause injury.
• But due to touch receptors in the skin which have the specialised tips of some nerve cells, due to which there is instant sensation of heat.
• We therefore, withdraw the hand in response to touching a hot object.