Reproduction (WAEC) PDF

Parts of a flower 1. Sepals (calyx): Sepals are normally green. It protects the flower while it is a bud. 2. Petals (corolla): These are often brightly coloured. The petals attract insects to the flower. Some petals possess lines called guide lines which guides the insects to the base of...

Parts of a flower 1. Sepals (calyx): Sepals are normally green. It protects the flower while it is a bud. 2. Petals (corolla): These are often brightly coloured. The petals attract insects to the flower. Some petals possess lines called guide lines which guides the insects to the base of the petal where nectar (a sugary fluid) is made in the nectary gland. 3. Stamens: Inside the petals are the stamens. These are the male parts of the flower. Each stamen is made of a long filament (a stalk which holds the anther) with an anther at the top. The anther contains pollen grains which contain the male gametes 4. Carpel: This is the female part of the flower located in the centre. A carpel contains an ovary with many ovules which contain the female gametes. At the top of the ovary is the style ( a stalk holding the stigma) with a stigma at the tip. The function of the stigma is  POLLINATION Pollination is the transfer of pollen grains from the anther to the stigma of a flower Self-pollination: This is the transfer of pollen grains from the anther to the stigma of the same flower or a different flower on the same plant Advantages of self-pollination Increases greater chance of pollination There is less wastage of pollen/gametes It does not require pollinating agents It brings about variety that is well adapted to the environment It is very useful if there is no other plants of the same species nearby Disadvantages There is less variation Plants are more susceptible to diseases There is less chance of adapting to changing conditions  Cross-pollination: This is the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species  Advantages of cross-pollination  It leads to production of more seeds  It produces healthier seeds  Plants are more likely to survive changes in environmental conditions since their genetical products are mixed  It leads to greater variations among species and a faster rate of evolution  Disadvantages  It is less certain to occur since it involves two separate plants which may be at greater distance  Pollen grains are likely to be wasted in the process  Cross-pollinated flowers are often more complicated in structure than self-pollinated flowers and often require special mechanisms.  CONDITIONS OR DEVICES THAT AID SELF  POLLINATION. Homogamy: This is when the anther and the stigma of a bisexual flower ripen at the same time.  Cleistogamy: This is a condition ripe pollen grains are deposited on the stigma which becomes ripen at the same time. This situation usually occurs in closed flowers that do not open at all. CONDITIONS OR DEVICES THAT AID CROSS POLLINATION.  Dichogamy: 1. Protandry (When anther matures before stigma) 2. Protogyny (When stigma matures before anther)  Unisexuality  Self sterility  Presence of nectar  Presence of conspicuous, brightly coloured petals  Possession of scent  Features of insect- pollinated flowers 1. Possess large, brightly coloured, conspicuous petals usually with guide lines 2. Anthers are located inside the flower, where insect has to brush past it to reach the nectar 3. Stigma is located inside the flower, where insect has to brush past it to reach the nectar 4. Pollen grains are sticky so can stick to insect. 5. It is often strongly scented 6. It has nectary at the base of the petal. 7. They have quite large quantities of pollen grains made because some will be eaten or delivered to the wrong kind of flower.  Features of wind- pollinated flowers 1. Possess small, with inconspicuous petals or no petals at all 2. Anthers are dangling outside the flower, where the pollen grains are carried by the wind. 3. Stigmas are large and feathery and dangling outside the flower, where pollen in the air may land on it 4. Pollen grains are smooth and light which can be blown in the wind 5. Possess no scent 6. Possess no nectaries  They have very large quantity of pollen grains made because most will be blown away and lost  DOUBLE FERTILIZATION IN FLOWERING PLANTS  After pollination, the pollen grain absorbs a sugary fluid on the stigma, swells and germinates. The exine splits while the intine grows into the pollen tube  Initially, the pollen grain has one nucleus. Later, this nucleus splits into two ( a large tube nucleus and a small generative nucleus)  The generative nucleus divides into two male gametes.  The tube nucleus controls the growth of the pollen tube through the style to the ovary  The pollen tube grows into the ovule through the micropyle. The tip of the pollen tube bursts and the two male gametes are released into the embyo sac.  One male gamete fuses with the ovum to form the zygote. SEED: Seed is a fertilized ovule.  PARTS OF A SEED  -Testa: A covering which protects the embryo from being damaged prevent bacteria and fungi from entering the seed.  -One scar called hilium( a point where the seed is joined to the ovary).  - Micropyle: is a tiny hole on the testa where oxygen and water enter the seed.  -Embryo: consists of radicle and plumule.  -Cotyledon: for food storage. In dicot plant e.g. bean seed, food is stored in two cream-coloured cotyledons. These contain starch and protein. In monocot plant e.g. maize grain, food is stored in a special tissue called endosperm which is outside the cotyledon. Label the following parts  SEED  DORMANCY This is the period when embryo of a develop seed is inactive.  Dormancy helps seed to survive harsh conditions such as cold or drought which would kill a growing plant. Seed Germination Germination is the development of seed into a new young plant/seedling. Process of Germination -Amylase and protease in the cotyledon become active by the -For a seed to water, breaking the stored starch - As the water goes into maltose(converted to glucose germinate, it first into the cotyledons, to make cellulose for cell wall in takes up water new cells and for respiration to they swell. Eventually, generate energy) and protein into through the amino acid(used to make new they burst the testa. micropyle. protein molecules for cell membranes and cytoplasm) respectively. -then, radicle appears and grows -soluble nutrients downwards into the (glucose and amino soil while the acid) diffuse into the plumule grows embryo upwards above the soil. Conditions for germination.  Water  Oxygen  Suitable temperature/warmt h  Enzymes  Food  Viable seed Types of Germination -Hypogeal germination -Epigeal germination Experiment to demonstrate the conditions needed for germination  AIM  MATERIALS REQUIRED  PROCEDURE  OBSERVATION  CONCLUSION  DISPERSAL OF FRUIT AND SEEDS Dispersal is the scattering of fruits and seeds to different directions from the parent plant. The function of fruit is to protect the seed inside it until they are ripe and then to help disperse the seeds. Reasons for dispersal  To prevent overcrowding of plants.  To reduce the degree of unhealthy competitions among plants.  To introduce the plant species into new environments where they may be better adapted. Agents of dispersal Wind Animals Water Explosive mechanism REPRODUCTION IN HUMANS FEMALE REPRODUCTIVE SYSTEM. The parts of the female reproductive system in human are:  Cervix: This is a ring of muscle separating the vagina from the uterus.  Ovary: It contains follicles in which ova or egg cells are produced.  Oviduct: It carries ovum to the uterus, with propulsion provided by tiny cilia in its wall. This is also the site of fertilization.  Uterus : This is where foetus develops. It is about 80mm long.  Vagina: This receives the penis during sexual intercourse. Sperm is  THE MALE REPRODUCTIVE SYSTEM The parts of the male reproductive system in human are:  Epididymis: It stores sperm before ejaculation.  Scrotum: A sac that holds the testis outside the body, keeping them cooler than body temperature.  Testis: This is the male gonad that produces sperm. Also, it is the site meiosis.  Prostate gland: It adds fluid and nutrients to sperm to aid swimming.  Seminal vesicle: It adds fluid and nutrients to sperm to form semen.  Urethra: A urinogenital structure that carries both urine and semen from bladder and sperm duct respectively to outside the body.  Sperm duct or Vas deferens: This carries sperm to urethra. It is either tied or cut during vasectomy.  Penis: It introduces the sperm into the vagina. Production of Gametes Sperm Production. The lining of the sperm producing tubules (seminiferous tubules) in the testis consists of rapidly dividing cells. After a series of cell divisions, the cells grow long tails called flagella and become sperm which pass into epididymis. The production of sperm cells is called spermatogenesis. Egg or Ovum Production  -Partly developed egg cells are present in a girl’s ovaries from the time of birth. Therefore, no more are formed during the female lifetime.  -When a girl child reaches puberty (usually between the ages of 10 to 14), some of these eggs begin to mature. Usually only one egg develops at a time and is released every four weeks from alternate ovaries.  -As each ovum matures, it divides by meiosis and the cells around it produce a fluid-filled sac called follicle.  -When fully mature, the follicle bursts, releasing an egg cell out of the ovary into the oviduct. This is called ovulation.  The production of egg cells is called oogenesis.  STRUCTURE OF SPERM Sperm is 0.05mm long. It contains the following parts.  Head: This is made of: 1. Nucleus: It contains chromosomes and male genetic information. 2. Acrosome: A vesicle containing enzymes used to dissolve a way through the jelly coat surrounding the egg cell or ovum.  Middle Piece: This contains 3. Mitochondrion: It releases energy for spermatozoa to swim to the egg cell.  Tail: 4. Flagellum: Aids swimming or movement of the sperm.  STRUCTURE OF EGG CELL OR OVUM. Ovum is 0.1mm in diameter and contains the following:  A large cytoplasm: This is rich in fats and proteins. The fats provide energy while proteins are available for growth if the egg is fertilized.  Nucleus: It contains chromosomes and female genetic information.  Plasma membrane  FERTILIZATION Once sperm are deposited into the vagina, they swim through the cervix into the uterus by the wriggling movement of their flagella They pass through the uterus and enter the oviduct. If there is an ovum in the oviduct, one of the sperm my bump into it and stick to its surface. The acrosome at the head of the sperm secretes enzymes which digest part of the egg membrane or jelly coat. Only the head of the sperm enters the cytoplasm of the ovum and the tail left outside. Male nucleus of the sperm fuses with the female nucleus to form a zygote. As soon as the successful sperm enters, the egg membrane becomes impenetrable, so that no other sperm can get in. The unsuccessful sperm will all die.  IMPLANTATION  After fertilization, the zygote continues to move slowly down the uterus, divides by mitosis into two cells.  --Each of these cells divides again to produce four cells. The cells continue to divide in this way to produce a solid ball of cells called embryo which obtains food from the egg yolk.  -This early embryo travel down the oviduct to the uterus where it sinks into the lining of the uterus, a process known as implantation.  PREGNANCY -Soon after the ball of cells reaches the uterus, some of the new cells instead of forming organs of the embryo grow into a dis-like structure called placenta. The embryo continues to grow, producing new cells that form tissues and organs.  The placenta becomes closely attached to the lining of the uterus and connected to the embryo by a tube called umbilical cord (it contains artery and vein)  -As the embryo grows, the uterus enlarges to contain it. Inside the uterus, the embryo becomes enclosed in a fluid-filled sac called amnion or water sac which secretes the amniotic fluid in which the fetus floats.  -At ten or eleven weeks after fertilization, all the organs are in place and embryo in the uterus is now called a fetus grows steadily until about thirty-eight weeks. FUNCTIONS OF AMNIOTIC SAC AND AMNIOTIC FLUID Amnion or Amniotic sac - It secretes amniotic fluid -It prevents entry of pathogens (from the vagina) Amniotic fluid -It supports foetus -It protects the foetus against damage or sudden movement or bump. -It provides constant temperature or protects against fluctuating temperature. -It allows fetus to move. -It is needed for bone or muscle growth and development. - It helps lungs or gut develop - It collects fetal urine or excretory waste products -It provides sterile environment. Functions of placenta  Prevention of maternal and fetal blood from mixing.  Protection against mother’s immune system.  Supply of oxygen to fetus.  Allows oxygen and nutrients (amino acids, glucose) from the mother’s blood to diffuse into the fetus’ blood.  Allows carbon dioxide and waste materials (urea) from the fetus’ blood to diffuse into the mother’s blood.  Protection of fetus against pathogens.  Transfer antibodies from mother to foetus.  It secretes hormones i.e. progesterone.  ANTE-NATAL CARE  Ante-natal care is the way a woman should look after herself during pregnancy so that birth will be safe and her baby is healthy. During this period the mother –to-be is checked:  To make sure she eat properly and perhaps advice to take more iron for haemoglobin formation and folic acid (a vitamin) than she usually does to prevent anaemia.  To ensure that her blood is free of nicotine and alcohol, because pregnant women who drink alcohol or smoke are prone to have babies with low birth weight who are more likely to be ill. Smoking may also make miscarriage more likely. Alcohol can cross the placenta to deform the foetus.  To give advice on food preparation to prevent food borne infections  To make sure she is not ill or infected. Labour and Birth -A few weeks before birth, the fetus comes to lie downwards in the uterus with head above the cervix. -When labour (birth) starts, the uterus begins to contract rhythmically. -Uterus contractions become stronger and frequent. -Then blood-tinged mucus is released. -Cervix gradually widens (dilates) enough to let the baby head pass through. -Amniotic sac breaks and fluid escape through the vagina. -Finally, muscular contractions of the uterus wall and abdomen push the baby head first through the cervix and vagina. -Placenta becomes a flat disc about 12cm in diameter and 3cm thick, breaks away from the uterus and pushed out separately as the afterbirth. -Umbilical cord is clamped and cut. After few days, remain of the umbilical cord attached to the baby’s abdomen shrivels and falls away leaving a scar on the abdominal wall called navel.  TWINS  Fraternal twins comes from two separate ova, each fertilized by a different sperm. It is possible to have a boy and a girl in this way.  Identical twins are formed from a single ovum and sperm. These twins share a placenta and amnion and must be of the same sex.  SEX HORMONES IN HUMANS 1. Testosterone: this is the male sex hormone. It is secreted by the testes.  -It causes the development of the following secondary sexual characteristics in boys:  *deepening of voice  * hair growth on face, body and pubic region.  *increased muscle development  *broad shoulder  * growth of genitals. 2. Progesterone and Oestrogen: These are the female sex hormones produced by the ovaries.  At puberty, increased secretion of Oestrogen causes the development of the following secondary sexual characteristics in girls:  -breast development-vagina, oviducts and uterus development  -hips widening  -hair growth on pubic region  -fat deposition.  METHODS OF BIRTH CONTROL IN HUMANS. The method of preventing the formation of a baby is called contraception. These methods are: NATURAL METHOD: This include: Abstinence Rhythm CHEMICAL METHOD: This involves the use of Contraceptive pill or injection. Spermicide Intrauterine system (IUS). MECHANICAL METHOD Use of Condom (female version is called femidom): Use of Diaphragm or Cap. SURGICAL METHOD Vasectomy Sterilization  NATURAL METHOD  Abstinence: This is the birth control method in which couple avoids sexual intercourse completely. It is the most reliable method but difficult to do.  Rhythm: This involves withdrawal of penis before ejaculation during three or four days before or after ovulation. The woman’s body temperature (which is normally higher than normal body temperature during ovulation) or quality of cervical mucus is used to monitor the period of ovulation.  It is an unsafe method of birth control because it is never possible to be 100% certain when ovulation is going to happen.  CHEMICAL METHOD  Contraceptive pill or injection. -This pill contains progesterone or mixture of progesterone and oestrogen. -Progesterone in the pill prevents ovulation by inhibiting the secretion of Follicle stimulating hormone and luteinizing hormone. Oestrogen inhibits Follicle Stimulating Hormone. -Pills are 99% effective but long term use may increase the risk of cancer of the breast and cervix.it does not protect against STIs.  Spermicide -Spermicide is chemical that kills sperm in the vagina. -It is quite easy to use but only effective when used in combination with diaphragm or cap.  Intrauterine system (IUS). -This is a T-shaped object that is fitted inside the uterus by a doctor or nurse. -It releases sex hormone that thickens the mucus from the cervix, making it difficult for sperm to swim into the uterus. -It does not protect against STIs.  MECHANICAL METHOD  Use of Condom (female version is called femidom): this prevents sperm from the vagina. It also prevents STIs transmission.  Use of Diaphragm or Cap: this is fits over the entrance of the cervix to stop sperm from entering the uterus. It does not prevent the risk of transmission of STIs. SURGICAL METHOD  Vasectomy: this means cutting of sperm ducts.  Tubular ligation: involves cutting the oviduct. REPRODUCTIVE STRATEGIES Oviparity  It is a reproductive method in which the female parent lays its egg, which may be fertilized internally or externally into the environment where it is hatched.  Viviparity  It Is a reproductive method in which fertilized eggs develop in the mother’s body, the embryo obtains its nutrients directly from the parent in addition to that present in the egg through the placenta and offspring is born alive. Ovoviviparity It is a reproductive strategy in which embryo develops in the egg that remains within the organism’s body until the egg is hatched or about to hatch. Embryo is nourished by the egg yolk rather than by the mother’s body. However, gaseous exchange is through Parts of an egg and their functions.  Yolk:- This provides digested food nutrients for the developing embryo.  Air space: Stores air for gaseous exchange.  Porous shell: Provides shelter or protects the embryo against mechanical damage.  Albumen: Absorbs shock.  Chalaza: Holds the yolk or embryo in position.  Shell membrane: For protection or gaseous exchange.  Other membranes include; (a) Amnion or amniotic sac– is the inner most membrane which secretes amniotic fluid. (b) Chorion – is the outermost membrane which controls permeability and prevents water loss from the amnion. (c) Allantois – Stores embryo’s nitrogenous waste and acts as gaseous exchange surface for the embryo.  Comparison of sexual reproduction in vertebrates Feature Fishes Amphibian Reptiles Birds Mammals s Number of egg Numerou Many One to forty One to Do not lay laid s twenty-five egg Fertilization Parental care Development of embryo  Comparison of sexual reproduction in vertebrates Feature Fishes Amphibian Reptiles Birds Mammals s Number of Numerous Many One to forty One to Do not lay egg laid twenty-five egg Fertilization External External Internal Internal Internal Parental care No parental No parental No parental Parental Parental care care care care care present present Development oviparity oviparity Oviparity and oviparity Viviparity of embryo ovoviviparity