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SS 3 Biology (1st Term)

Biology

DEVELOPMENT OF ZYGOTE IN FLOWERING PLANTS

DEVELOPMENT OF ZYGOTE IN FLOWERING PLANTS, GERMINATION OF SEEDS, ADAPTIVE FEATURES IN A DEVELOPING ANIMAL DEVELOPMENT OF ZYGOTE IN PLANTS Pollination is followed by fertilization and the development of zygote in flowering plants during which the flower changes into a fruit enclosing the seeds. The male and female sex cells that form zygote at fertilization are the pollen grain and the ovule. The following are the processes involved   After pollination – the pollen grain absorbs a sugary liquid on the stigma swells, and germinates. The outer coat of the pollen grain splits and the pollen tube grows out and down inside the style. The nucleus of the pollen grain divides into two – a large tube nucleus and a smaller generative nucleus .The male nucleus is the male gamete. One of the male nuclei – after their release into the embryo sac, fuses with the ovule to form a… Read More »DEVELOPMENT OF ZYGOTE IN FLOWERING PLANTS

Biology

DEVELOPMENT OF NEW ORGANISMS

COURTSHIP BEHAVIOURS IN ANIMALS Courtship is a reproductive communication between males and females of a species that ends in sexual union. Courtship behaviours in animals include PAIRING: – A form of courtship in which a compatible male and female separate themselves from other in a group to form a mating pair. Pairing occurs in human, toad, fish, winged termites etc. DISPLAY: – A process involving fixed pattern movements or attractive exhibitions and responses between a male and a female which ends in mating. Examples of display include croaking in toads, dancing, singing in human, production of odour by females, stunning tail feathers of a peacock etc. TERRITORIALITY: – A form of behavior in which a member of a specie marks out a fixed area and defend it against intruders of the same species. Usually males establish territories prior to mating. Territories are established by most vertebrates except amphibians. SEASONAL MIGRATION:… Read More »DEVELOPMENT OF NEW ORGANISMS

Biology

ORGAN OF HEARING, SMELL AND TASTE

THE ORGAN OF HEARING Mammals have two ears on each side of the head.  The greater part of it is enclosed in the skull for protection.  The ear is for hearing as well as for maintaining balance.   STRUCTURE OF THE EAR AND THEIR FUNCTIONS The mammalian ear is divided into 3 parts. The outer ear. The middle ear. The inner ear. The outer ear This is made up of the following from outside the organism: The Pinna: – This is flexible being made up of soft cartilage covered with skin. The pinna collects sounds, detects their direction and directs them into the canal called external auditory meatus (ear tube). External Auditory Meatus: – This consists of fine hairs and glands which produce wax. Therefore it prevents germs, insects and dusts from entering and affecting the ear. It allows the passage of sound waves from the pinna to the ear… Read More »ORGAN OF HEARING, SMELL AND TASTE

Biology

SENSE ORGANS

SENSORY RECEPTORS All living organisms respond to changes in their environment (stimuli).  These changes can be mechanical, electromagnetic, chemical or thermal.  Though most cells in the bodies of organisms are sensitive to stimuli, certain cells specialize in detecting a particular type of stimulus, these are called sense cells or sensory receptors which are quite many in human bodies, monitoring the internal environment. Sensory receptors sensitive to mechanical changes are called mechanoreceptors likewise thermoreceptors, chemoreceptors and photoreceptors are sensitive to heat, chemical and light respectively.   The sensory receptors change the detected stimulus into electrical impulses which when received by the brain are translated into pictures, sounds, smell, taste sensations. Structures containing sensory receptors are referred to as sense organs   A sense organ is defined as a group of specialized cells or tissues or which are able to receive, perceive or detect stimulus and transmit the information to the central… Read More »SENSE ORGANS

Biology

REFLEX, VOLUNTARY ACTIONS AND CONDITIONAL REFLEXES

REFLEX AND VOLUNTARY ACTIONS Actions are responses to stimuli. These actions are grouped into two: involuntary (reflex) and voluntary actions.   REFLEX ACTIONS Reflex actions are automatic responses to stimuli which do not involve the conscious or higher centre of the brain.   These actions are mainly protective, guarding us from dangerous stimuli and helping us to maintain posture and balance.  Reflex actions include jerking of the legs, blinking of the eyes etc.   THE REFLEX ARC The reflex arc involves the following: the sensory receptors that receive the stimulus. the sensory neurones along which the sensory impulse travels the relay or intermediate neurone through which the sensory impulse is passed on. the motor (efferent) neurones along which the response is transmitted. the effectors (muscles and glands) which the motor impulses trigger to bring about an appropriate response.   Reflex actions can be: Spinal reflex involving the spinal cord e.g knee… Read More »REFLEX, VOLUNTARY ACTIONS AND CONDITIONAL REFLEXES

Biology

THE PERIPHERAL NERVOUS SYSTEM

THE PERIPHERAL NERVOUS SYSTEM These include the sensory system (receptor and nerves leading from all parts of the body to the CNS) and the motor system (nerves running from the CNS to the effectors). The PNS consists of twelve cranial nerves (connecting the brain to the head and neck region) and thirty one spinal nerves (connecting the spinal cord to the thorax, abdomen and limbs). The motor system is subdivided into somatic and autonomic nervous system.   EVALUATION Differentiate between  the cranial and spinal nerves   SOMATIC AND AUTONOMIC NERVOUS SYSTEMS The SNS consists of motor (efferent) neurones that connect the CNS to each skeletal muscle. It serves the parts of the body which take part in responses to external stimuli and all voluntary actions.   The ANS consists of motor (efferent) neurones that connect the CNS to glands, smooth muscles and cardiac muscles. It regulates all the body’s involuntary… Read More »THE PERIPHERAL NERVOUS SYSTEM

Biology

NERVOUS CO-ORDINATION

THE NERVOUS SYSTEM The nervous and hormonal systems co-ordinate various biological activities in the body of multicellular animals, the basic structural unit of nervous system is the nerve cell called neurone.  It consists of a dense, cell body and protoplasmic processes called nerve fibres.  A bundle of long nerve fibre is called a nerve.  The main mechanism of information transfer is electric impulses known as nerve impulses along the nerve fibres. All the nervous systems in complex animals have the following: The central processing region (the brain) The nerves bringing impulses from receptors to the brain. Nerves carrying information from the brain to the effectors. Sensory receptors detect stimuli from the external and internal environment and so act as information collectors.  They are often found in the sense organs.  Effectors include muscles and glands that go into action on receiving nerve impulses from the brain.  Such actions include muscular contraction,… Read More »NERVOUS CO-ORDINATION

Biology

HORMONAL CO-ORDINATION

HORMONES AND ENDOCRINE GLANDS Hormones are chemical substances produced or secreted by endocrine glands (ductless glands) in response to various stimuli. Hormones are secreted into the bloodstream and circulated to exert their effect on their target organs.  This effect could be to speed up or slow down biological reactions. A few hormones like thyroxine and other growth hormones exert their effects on all body cells.  A hormone can therefore be defined as a chemical messenger that is produced in one part of an organism and brings about a specific effect in a target organ some distance away. Hormones (usually needed in small amount) are active in homeostasis, growth and development. After their actions, hormones are inactivated in the liver and excreted in urine.   EVALUATION What is hormone? State four characteristics of hormones   ANIMAL HORMONES There are basically five groups of animal hormones which are secreted by different glands… Read More »HORMONAL CO-ORDINATION

Biology

LIVER AND SKIN: STRUCTURE, FUNCTIONS, DISEASES AND CARE

STRUCTURE OF THE LIVER The liver is the largest organ in the body of a mammal with a weight of about 1.25kg.  It is reddish brown, soft with two lobes and it is located below the diaphragm on the right side of the abdomen.  It partly overlaps the stomach and has bile duct connecting it to the duodenum.  The duct is attached to the gall bladder.   FUNCTIONS OF THE LIVER Regulation of blood glucose level by converting excess glucose to glycogen under the control of the hormone insulin. With low glucose level, glycogen is converted to glucose under the influence of hormone, glucagon. Both insulin and glucagon are produced by the pancreas. Regulation of blood protein. The body cells cannot store excess amino acids in the body.  The liver therefore deaminates excess amino acids by breaking them down into amino group (converted to urea for excretion) and carboxyl group… Read More »LIVER AND SKIN: STRUCTURE, FUNCTIONS, DISEASES AND CARE

Biology

REGULATION OF INTERNAL ENVIRONMENT

HOMEOSTASIS Homeostasis is the process by which a fairly constant internal environment is maintained in an organism.  The internal environment of an organism is made up of the body fluid such as blood, lymph and tissue fluid.  For efficient functions of body cells and healthy growth, a living organism must be able to adjust to any change in the physical and chemical conditions of its body fluids.  These conditions include temperature, PH, osmotic pressure, concentrations of dissolved substances and mineral ions.   MECHANISM OF HOMEOSTASIS Homeostatic processes are control mechanisms which are used to detect and adjust to changes in the internal environment of the organism. These mechanisms usually include: Sensory detectors which recognize a change in a given condition and stimulate the relevant body parts. Effectors organs or glands which react and restore the normal state.   STRUCTURES FOR HOMEOSTASIS Osmoregulation (homeostasis) in unicellular organism is ensured by the… Read More »REGULATION OF INTERNAL ENVIRONMENT

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