asexual and sexual reproduction
1) Define Asexual Reproduction
- A process resulting in the production of genetically identical offspring from one parent.
Examples:
Bacteria
- Reproduce by binary fission, each bacterium divides into two.
- The generation time is the time taken for a cell to divide into 2.
Fungi
- Single-celled yeast reproduces by binary fission.
- All other fungi produce via spores.
- When the sporangium bursts it spreads the spores.
- Spores land and grow mycelium (roots) for example mushrooms.
Potatoes
- The shoot from a potato goes back underground and the stem swells to form a new genetically identical potato.
- The swollen stem acts as a storage organ.
2) Advantages and Disadvantages of Asexual Reproduction
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3) Define Sexual Reproduction
- A process involving the fusion of the nuclei of two haploid gametes (sex cells) to form a diploid zygote and the production of offspring that are genetically different from each other.
4) Discuss the Advantages and Disadvantages of Sexual Reproduction
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sexual reproduction in plants
5) Parts and Functions of an Insect Pollinated Flower
- Sepal: protect the flower bud.
- Petal: brightly coloured and scented and may have nectarines which are all used to attract insects, petals in wind pollinated flowers are tiny.
- Anther: has pollen sacs with pollen grains which contain the male nucleus (male gamete).
- Stigma: the female part of the plant which collects pollen from insects or from the air. In wind-pollinated plants, the stigmas and anthers hang out of the plant where they are more exposed to the wind.
- Ovary: hollow chamber, ovules grow from the walls.
6) Define Pollination
- Transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma).
Cross-pollination:
- Occurs when grains of pollen are transferred from the anthers of one flower to the stigma of another flower of the same species.
Agents of Pollination:
- Insects
- Birds
- Bammals
- Water
- Wind
* 7) Discuss the implications of Self-Pollination and Cross-Pollination
- Self pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant.
- Cross pollination 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.
Cross-pollination:
- Guarantee variation.
- Better chance of adapting to changing conditions.
- Reliance on pollinators to carry the pollen to other plants.
Self-pollination:
- No variation.
- Not be able to adapt to changing environmental conditions.
- No reliance on pollinators.
8) Distinguish between the Pollen Grains of Insect-Pollinated and Wind-Pollinated Flowers
- Pollen that is carried by insects is adapted to be sticky and have hooks which attach to the insect.
- Pollen carried by the wind does not need to stick to anything, thus is smooth. It is also very light.
9) Describe the Structural Adaptations of Insect-Pollinated and Wind-Pollinated flowers
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* 10) Describe the Growth of the Pollen Tube
- When a pollen grain lands on the stigma of a flower of the correct species, a pollen tube begins to grow.
- It grows down the style and into the ovary, where it enters a small hole, the micropyle, in an ovule.
- The nucleus of the pollen then passes along the pollen tube and fuses with the nucleus of the ovule.
- This process is called fertilisation.
11) State the Environmental Conditions that affect Germination of Seeds
- A process controlled by enzymes
- Water: activates enzymes to turn insoluble food stores into soluble substances, and makes tissues swell so that the testa (seed coat) splits.
- Oxygen: enters through the gaps in the testa (along with water), and is used in aerobic respiration.
- Temperature: must be suitable for enzymes to work (at optimum temperature).
sexual reproduction in human
12) State the Functions of the Parts of the Male Reproductive System
- Testes: production of male gametes (sperm).
- Scrotum: sac that holds the testes outside the body.
- Sperm ducts: transfer sperm to the urethra.
- Prostate gland: secrete fluids for sperm to swim in forming semen.
- Urethra: carries urine and semen out of the body.
- Penis: transfers semen to vagina during sexual intercourse.
13) State the Functions of the Parts of the Female Reproductive System
- Ovaries: release of female gametes (eggs)
- Oviducts: transfers egg to uterus and the site of fertilisation
- Uterus: where the fetus develops
- Cervix: ring of muscle at the opening of the uterus
- Vagina: receives penis during sexual intercourse
14) Describe Fertilisation
- Fertilisation is the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell/ovum).
- In plants, fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
- In human, fertilisation occurs when the nuclei from a male gamete (sperm) fuses with a female gamete (egg cell/ovum).
15) Compare Male and Female Gametes
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Sperm cells:
Egg cells:
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source: lifeeasy
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16) State the Development of the Zygote
- Once a sperm nucleus has successfully fused with the egg nucleus, the egg membrane alters to form barrier against more sperm
- The fusion of an ovum and a sperm forms a zygote.
- Zygote starts to divides over and over by mitosis, to make a ball of cells called an embryo.
- It travels down the oviduct and implants itself in the wall of the uterus.
17) Key Structures that support Development of Foetus
- After eight weeks of development, the embryo is called a foetus.
- The amniotic sac produces amniotic fluid, which surrounds and protects the developing embryo.
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- Umbilical cord: contains umbilical artery which carries deoxygenated blood and waste products from foetus to placenta and umbilical vein which carries oxygenated blood and soluble food from placenta to foetus. Contains foetus' blood.
- Placenta: organ for exchange of soluble materials such as foods, wastes and oxygen between mother and foetus; physical attachment between uterus and foetus. Contains mother’s blood.
- Amniotic sac: membrane which encloses amniotic fluid, broken at birth.
- Amniotic fluid: protects foetus against mechanical shock, drying out and temperature fluctuations.
- Mother passes essential nutrients to foetus through the umbilical cord, to help build cells and structures in foetus.
- Also passes antibodies to allow foetus develop resistance to pathogens.
- Waste products diffuse out of foetus to be excreted from the mother's body.
- Blood of foetus and mother do not mix.
- Toxins such as nicotine and pathogens can pass from other to foetus.
* 18) Describe the Antenatal Care of Pregnant Women
- Antenatal” or “prenatal” refers to the period before birth.
- Antenatal care is the way a woman should look after herself during pregnancy, so that the birth will be safe and her baby healthy.
- Eat properly, take more iron and folic acid (a vitamin) to prevent anaemia.
- Calcium for bone growth of mother and foetus.
- Drinking or smoking are more likely to cause babies with low birth weights. These babies are more likely to be ill than babies of normal birth weights.
* 19) Outline the Processes in Labour and Birth
- The period from fertilization to birth takes about 38 weeks in humans. This is called the gestation.
- A few weeks before the birth, the baby turns with its head just above the cervix.
- Uterus starts to contract rhythmically (labour).
- Rhythmic contractions become stronger and more frequent. The amniotic sac breaks at some stage in labour and the fluid escapes through the vagina.
- Cervix gradually widens (dilates) enough to let the baby’s head pass through and the contractions of the muscles in the uterus wall are assisted by muscular contraction of the abdomen.
- Muscular contractions of the uterus wall and abdomen push the baby head-first through the widened cervix and vagina.
- The umbilical cord, which still connects the child to the placenta, is tied and cut.
- Placenta breaks away from the uterus and is pushed out separately as the ‘afterbirth’.
* 20) Discuss Advantages and Disadvantages of Breast-Feeding
- Breastfeeding allows antibodies to be passed from the mother to the child to provide immunity.
- Breastfeeding no risk of an allergic reaction to breastmilk.
- Breastfeeding may be painful for the mother.
- Breastfeeding can only occur when the mother is present.
sex hormones in human
* 21) Describe the Role of the Testosterone and Oestrogen
- Testosterone is produced in the testes of males, and in small amounts in the ovaries of females. It is responsible for muscle development and the deepening of the voice, amongst other things.
- Oestrogen is made in the ovaries of females. It leads to the development of widened hips, breasts, and plays a part in the menstrual cycle.
22) Describe the Menstrual Cycle
- The menstrual cycle happens approximately every 28 days.
- During each cycle, an egg cell is released from the ovaries.
- The uterus wall thickens by filling with blood capillaries in preparation for a pregnancy, which would occur if the egg is fertilised.
- If this egg is not fertilised, the egg dies and menstruation occurs, where the dead egg cell and old uterus lining is expelled from the body in a period.
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- Stage 1: bleeding starts. The uterus lining breaks down and is released.
- Stage 2: the lining of the uterus builds up again, from day 4 to day 14, into a thick spongy layer of blood vessels ready to receive the fertilised egg.
- Stage 3: An egg is released from the ovary (ovulation) at about day 14.
- Stage 4: The lining is then maintained for 14 days, until day 28. If no fertilised egg has landed on the uterus wall by day 28 then the spongy lining starts to break down again and the whole cycle starts over.
* 23) Explain the Role of Hormones in Controlling the Menstrual Cycle
The menstrual cycle is regulated by four hormones:
- FSH: Follicle Stimulating Hormone triggers the development of an egg cell in the ovary, and also stimulates oestrogen production in the ovaries. This is produced in the pituitary gland.
- LH: Luteinising Hormone triggers an egg to be released, as well as stimulating progesterone production in the ovaries.
- Progesterone: is responsible for maintaining the thick uterus lining in the cycle and during pregnancy. It also decreases FSH production.
- Oestrogen: stimulates LH production, whilst decreasing FSH production.
* methods of birth control in human
24) Out line the Methods of Birth Control
Birth control is used in family planning to control when, and how many, children are produced.
- Natural birth control methods: these methods use the knowledge of the menstrual cycle to avoid pregnancy. This is done by monitoring body temperature and cervical mucus to predict when ovulation is occurring and avoiding sexual intercourse in this period. As cycles can be irregular and difficult to accurately predict, this method is not always reliable. Another natural method is to abstain from sexual intercourse.
- Chemical methods: chemical methods include the contraceptive pill, implant and injection, as well as IUD and IUS. These contain hormones which stop pregnancy. The contraceptive pill contains the hormones progesterone and oestrogen, which prevents ovulation. The contraceptive implant, injection and IUS both release progesterone and cause the uterus lining to thin, preventing the fertilised egg from implanting in the uterus wall. IUD also prevents implantation of the egg by thinning the uterus lining, and also acts as a physical barrier to stop sperm reaching the egg.
- Barrier methods: this includes the condom, femidom and diaphragm. These are used to act as a physical barrier and prevent the sperm from reaching the egg. Condoms also have the advantage of preventing the spread of STIs.
- Surgical methods: these procedures prevent the release of sperm and egg cells. A vasectomy involves the sperm ducts being tied or cut, preventing sperm from exiting the testes. In women, the oviducts can be tied or cut to prevent the release of egg cells from the ovaries.
25) Outline the use of Hormones in Contraception and Fertility Treatment
- Fertility treatments: On the other hand, there are also people who would like to have children who have difficulty becoming pregnant. In vitro fertilisation (IVF) and artificial insemination (AI) are two fertility treatments which can solve this:
- IVF: If fertilisation cannot occur due to the sperm count or quality being too low, the egg cell can be fertilised outside of the body and then be implanted back into the uterus.
- AI: sperm is directly inserted into the uterus. This sperm can be from the partner, or from a sperm bank if their sperm is not of a high enough quality.
26) Discuss the Social Implications of Contraception and Fertility Treatment
- Some people believe that fertility treatments, such as IVF, and genetic screening of embryos may lead to ‘designer babies’, where parents will discard eggs which do not have desired characteristics, for example a certain hair colour or gender. In addition, they may avoid having a child with an inherited disease.
- Some religious groups do not agree with artificial methods of contraception. This is because they believe that they are preventing a life that otherwise would have been created, which goes against their beliefs.
- Fertility treatments are also contentious as during IVF, multiple eggs are taken and fertilised at once, leading to spare embryos which are afterwards frozen and stored or destroyed.
sexually transmitted infections
17) Describe the methods of transmission of HIV
- Sexually transmitted infections, known as STIs, are infections that are transmitted via bodily fluids during sexual intercourse or contact.
- Human immunodeficiency virus (HIV) is an example of an STI.
- HIV is present in the bodily fluids of infected people, such as blood and semen, and can be transmitted during sexual intercourse.
- In the blood, HIV attaches to lymphocytes (white blood cells) and enters the cell.
- Here, it uses the cell to replicate itself and thus the cell cannot carry out its normal functions.
- Consequently, HIV reduces the number of functioning lymphocytes, as well as reducing the body’s ability to produce antibodies to fight off infection.
- HIV leads to Acquired Immune Deficiency Syndrome (AIDS), which makes the person extremely susceptible to other pathogens as the white blood cells can no longer fight off disease, which can be fatal.
Transmissions:
- Intercourse.
- Blood transfusion.
- Organ transplant.
- Sharing needle with infected person.
Prevention:
- Avoid intercourse with many partners.
- Use a condom.
- Don’t come in contact with other people’s blood.
