CHAPTER 4 HEREDITY AND EVOLUTION
CHAPTER 3 HOW DO ORGANISMS REPRODUCE?
The basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. The DNA copies eventually separate, each with its own cellular apparatus. A cell, therefore, divides to give rise to two cells.
MODES OF REPRODUCTION USED BY SINGLE ORGANISMS
For unicellular organisms, cell division, or fission, leads to the creation of new individuals. Many different patterns of fission have been observed. Many bacterial and protozoa simply split into equal halves during cell division. In organisms such as amoeba, the splitting of the two cells during division can take place in any plane.
However in some unicellular organisms, binary fission occurs in a definite orientation in relation to these structures. Other unicellular organisms divide into many daughter cells simultaneously by multiple fission.
In multi-cellular organisms with relatively simple body organisation, simple reproductive methods can still work. For e.g. Spirogyra simply breaks up into smaller pieces upon maturation. These fragments grow into new individuals.
Many organisms have the ability to give rise to new individual organisms from their body parts. For e.g. Simple animals like Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is called regeneration. Regeneration is carried out by specialized cells.
Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
5. Vegetative Propagation
In this method, parts like the root, stem and develop into new plants under appropriate conditions.
6. Spore formation
Spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
All these methods listed above are asexual mode of reproduction.
In sexual reproduction, two individuals are involved in the reproduction process. It incorporates the process of combining DNA from two different individuals during reproduction.
Sexual reproduction in flowering plants
Stamens and carpels are the reproductive parts of a flower which contain the germ cells. Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour. Carpel is the female reproductive part and it is present in the centre of the flower. It is made up of three parts. The swollen bottom part is the ovary, middle elongated part is the style and the terminal part which may be sticky is the stigma. The pollen needs to be transferred from the stamen to the stigma where the male germ cell produced by the pollen grain fuses with the female gamete present in the ovule which is contained in the ovary.
Sexual reproduction in humans
Changes in the body during puberty are signs of sexual maturation. The male reproductive system in human beings consists of testes, vas deferens, seminal vessels, prostate glands, urethra and penis. The testes are responsible for producing sperms. The female reproductive system in human beings consists of ovaries, fallopian tubes, uterus and vagina. Sexual reproduction in human beings involves the introduction of sperm in the vagina of the female. Fertilisation occurs in the fallopian tube.
Contraception to avoid pregnancy can be achieved by the use of condoms, oral pills, copper-T and other methods.
CHAPTER 2 CONTROL AND COORDINATION
In animals, control and coordination are provided by nervous and muscular tissues. All the information from our environment is detected by the specialised tips of nerve cells. These receptors are located in our sense organs. The information, acquired at the end of the dendritic tip of a nerve cell, sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron. This is how nervous impulses travel in the body.
Reflex is some sudden action in response to something in the environment. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain.
The brain is the main coordinating centre of the body. The brain sends messages to muscles. The communication between of the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.
The brain has three major parts or regions: the fore-brain, mid-brain and hind-brain.
The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on. Based on the information received by from all these receptors, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles.
Many involuntary actions are controlled by the mid-brain and the hind-brain. A part of the hind-brain called the cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance of the body.
COORDINATION IN PLANTS
Plants use electrical-chemical means to convey information from cells to cells. Some cells must change shape in order for movement to happen. Plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.
HORMONES IN ANIMALS
Hormones produced in one part of an organism move to another part to achieve the desired effect.
A feedback mechanism regulates the action of the hormones.
CHAPTER 1 LIFE PROCESSES
The processes which perform the maintenance functions in an organism are called life processes. These processes require energy which comes from outside the body of the individual. This energy comes from the food that the organism consumes which provided nutrition.
The process to transfer a source of energy from outside the body of the organism to the inside is called nutrition. The different modes of nutrition are:
1. Autotrophic nutrition
NUTRITION IN HUMANS
Humans are heterotrophs. Food is first crushed with the teeth to break it down into small pieces. From the mouth, the food is taken to the stomach through the food pipe. The stomach is a large organ which expands when food enters it. The stomach has muscular walls which help in mixing the food thoroughly with digestive juices.
The exit of the food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine. The small intestine is excessively coiled. It is the site of the complete digestion of carbohydrates, protein and fats with the help of secretions it receives from the liver and pancreas. The digested food is taken by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi in order to increase the surface area for absorption.
The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is removed from the body via the anus.
The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Breaking down glucose into a three carbon molecule called pyruvate. This pyruvate can be further broken down. If this occurs in the presence of air, it is called aerobic respiration and in the absence of air, it is called anaerobic respiration.
Human respiratory system
Air is taken into the body through the nostrils. The air passing through the nostrils is filtered by fine hairs that line the passage. The air then passes through the throat and into the lungs. Within the lungs the passage divides into smaller and smaller tubes which finally terminate in balloon like structures called alveoli. The respiratory pigments take up oxygen from the air in the lungs and carry it into the tissues which are deficient in oxygen.
In human beings, the transport of materials such as oxygen, carbon dioxide, food and excretory products is the function of the circulatory system. The circulatory system consists of the heart, blood and the blood vessels.
In plants, transport of water, minerals, food and other materials is a function of the vascular tissue which consists of xylem and phloem.
The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. The urine produced in the kidney’s passes through the ureters into the urinary bladder where it is stored until it is released through the urethra. Nitrogenous waste such as urea or uric acid are removed from blood in the kidneys
The excretory system of plants is completely different from that of the animals. They get rid of excess water by transpiration. Waste products can also be stored in leaves that fall off. Other waste products can be stored as resins and gums, especially in old xylem. Plants can also excrete some waste into the soil around them.