B8 Revision Notes

8.1 - Asexual and sexual reproduction
1. Define asexual reproduction.
The process resulting in the production of genetically identical offspring from one parent.
2. Discuss the advantages and disadvantages to a species of asexual reproduction.
 The process is quick;
 Only one parent is needed;
 No gametes are needed;
 All the good characteristics of the parent are passed on to the offspring;
 They usually store large amounts of food that allow rapid growth when conditions
are suitable
 There is little variation created, so adaptation to a changing environment (evolution)
is unlikely;
 If the parent has no resistance to a particular disease, none of the offspring will have
 Lack of dispersal (e.g. potato tubers) can lead to competition for nutrients, water and
3. Define sexual reproduction.
The process involving the fusion of haploid nuclei to form a diploid zygote and the
production of genetically different offspring.
4. Discuss the advantages and disadvantages to a species of sexual reproduction.
 There is variation in the offspring so adaptation to a changing or new environment is
likely, enabling survival of the species;
 New varieties may be created which may have resistance to disease;
 In plants, seeds are produced, which allow dispersal away from the parent plant,
reducing competition;
 Two parents are usually needed (although not always- some plants can selfpollinate);
 Growth of a new plant to maturity from a seed is slow.
8.2 - Sexual reproduction in plants
1. Identify and draw, using a hand lens if necessary, the sepals, petals, stamens, anthers,
carpels, ovaries and stigmas of one locally available, named insect-pollinated,
dicotyledonous flower, and examine the pollen grains under a light microscope or
Insect pollinated, dicot. flower.
And the pollen grains.
2. Use a hand lens to identify and describe the anthers and stigmas of one locally
available, named, wind-pollinated flower.
B-Feathery stigma,
C-Anther loosely attached
to the filament, D- Ovary
Figure showing wind-pollinated flower
3. State the functions of the sepals, petals, anthers, stigmas and ovaries.
Petiole (stalk)
Often large and coloured, to attract insects
Protects the flower while in bud
Supports the flower to make it easily seen by insects, and to be able to
withstand wind
The male reproductive part of the flower, made of anther and filament
Contains pollen sacs, in which pollen grains are formed. Pollen contains
male sex cells
Supports the anther
The female reproductive part of the flower, made of stigma, style and ovary
A sticky surface that receives pollen during pollination
Links the stigma to the ovary, through which pollen tubes grow
Contains ovules, which develop into seeds when fertilised
4. Candidates should expect to apply their understanding of the flowers they have
studied to unfamiliar flowers.
5. Define pollination.
Transfer of pollen grains from the male part of the plant (anther) to the female part (stigma).
6. Name the agents of pollination.
Wind; Animals including insects; Water
7. Compare the different structural adaptations of insect-pollinated and wind-pollinated
Present- often large, coloured
and scented
Produced by nectaries to attract
Present inside the flower
Small surface area, inside the
Smaller amounts- grains are
often round and sticky, or
covered in spikes to attach to the
furry bodies of insects
Absent or small and inconspicuous
Absent, or small and green
Long filaments, allowing the anthers
to hang freely outside the flower so
the pollen is exposed to the wind
Large and feathery, hanging outside
the flower to catch pollen
Larger amounts of smooth and light
pollen grains, which are easily
carried by the wind
Sometimes present
8. Investigate and state the environmental conditions that affect germination of seeds:
requirement for water and oxygen, suitable temperature.
IGCSE Biology (Jones & Jones), p.190, activity 13.4 – ‘to find the conditions necessary for the
germination of tomato seeds’.
Environmental conditions affecting germination
Environmental condition
Suitable temperature
Absorbed through micropyle, needed to activate enzymes
which convert insoluble food stores into soluble foods needed
for growth and energy production.
Needed for respiration, to release energy for growth and
chemical changes for mobilization of food reserves
For enzymes to work as enzymes work best at optimum
Not usually a requirement for germination but some seeds
need a period of exposure to light before they germinate
9. Investigate and describe the structure of a non-endospermic seed in terms of the
embryo (radicle, plumule & cotyledons) and testa, protected by the fruit.
 After fertilization, the ovule becomes a zygote;
 The zygote divides by mitosis to form an embryo plant;
 The ovule is now called a seed;
 The ovary becomes the fruit.
Part of the seed
Tough protective
Food store
Part of embryo
Part of embryo
Tiny hole in testa
A scar near the
Stop embryo from being damaged,
prevents bacteria and fungi from
entering the seed
Contains starch, protein and enzymes
Grow into root
Grow into shoot
Water and oxygen enters the seed
through this hole
Where the seed was joined to the pod
10. State that seed and fruit dispersed by wind and by animals provides a means of
colonizing new areas.
 Dispersal of seeds is important, because it prevents too many plants growing close
 If this happens, they compete for light, water and nutrients, so that none can grow
 Dispersal also allows the plant to colonise new areas.
11. Describe, using named examples, seed and fruit dispersed by wind and by animals.
Wind dispersed fruit
 Dandelion fruit has a group of
fine hairs called a pappus;
 Pappus acts as a parachute and
catches wind;
 The fruit counterbalances the
 Sycamore has a wing with a large
surface area;
 When fruit drops of the tree it
spins, slowly down its descent;
 If caught by wind the seed will be
carried away from the parent
plant, reducing competition for
nutrients, water and light.
Animal dispersed fruit
Succulent fruits e.g. blackberry
 They are coloured, juicy and
nutritious and hence attracted by
 When eaten seeds pass through
the gut without getting digested
and deposited with animal faeces
far away from the parent plant.
Hooked fruits e.g. bur
 Catch on to animal’s fur as it
brushes past the parent plant;
 Eventually the seed drop off and
gets dispersed far away from the
parent plant.
8.3 - Sexual reproduction in humans
1. Identify on diagrams of the male reproductive system, the testes, scrotum, and sperm
ducts, prostate gland, urethra and penis, and state the functions of these parts.
Prostate gland
Seminal vesicle
Sperm duct
Testis (pl. testes)
A mass of tubes in which sperm are stored
Can become firm, to insert into the vagina of the female during
sexual intercourse, to transfer sperm
Adds fluid and nutrients to sperm, to form semen
A sac that holds the testes outside the body, keeping them cooler
than body temperature
Adds fluid and nutrients to sperm, to form semen
Muscular tube which links the testis to the urethra to allow the
passage of semen containing sperm
Male gonads that produce sperm
To pass semen containing sperm through the penis, also carries
urine from the bladder at different times
3. Identify on diagrams of the female reproductive system, the ovaries, oviducts, uterus,
cervix and vagina, and state the functions of these parts.
Funnel of oviduct
A ring of muscle that separates the vagina from the uterus
Directs an ovum (egg) from the ovary into the oviduct
Contains follicles in which ova (eggs) are produced
Carries an ovum to the uterus, with propulsion provided by
tiny cilia in the wall; also the site of fertilization
Carries urine from the bladder
Where the fetus develops
Receives the male penis during sexual intercourse; sperm are
deposited here
2. Compare male and female gametes in terms of size, numbers and mobility.
Types of gamete
1. Is large in size 0.1mm because it
has all cell components that is
needed for the cell to grow and
multiply; has yolk to nourish the
2. During ovulation, only one egg is
released every month.
3. Ovum is immobile as the sperm
moves towards it to fertilise it.
1. Size is very small 0.05mm.
2. During ejaculation millions of
sperms are produced into the
women’s vagina.
3. Sperms are highly mobile and can
swim towards the oviduct with he
help of its tail.
4. Describe the menstrual cycle in terms of changes in the uterus and ovaries.
5. Describe the fertilization in terms of the joining of the nuclei of male gamete (sperm)
and the female gamete (egg).
During sexual intercourse, erect penis is inserted into
Semen is ejaculated into the neck of vagina;
Many sperms cluster around ovum but only one
A fertilization membrane is secreted around the egg
once one sperm enters;
The sperm nucleus fuses with egg nucleus to form
zygote, this process is called fertilization.
6. Outline early development of the zygote simply in terms of the formation of a ball of
cells that becomes implanted in the wall of the uterus.
7. Indicate the functions of the amniotic sac and amniotic fluid.
Amniotic sac
Amniotic fluid
A thin membrane, formed from cells of embryo, contains the
amniotic fluid;
It encloses the fetus and prevents entry of bacteria.
Supports the fetus, protecting it from physical damage;
It absorbs excretory materials (urine) released by the fetus.
8. Describe the function of the placenta and umbilical cord in relation to exchange of
dissolved nutrients, gases and excretory products (no structural details are required).
 The placenta brings the blood supply of the fetus close to that of the mother, but
prevents mixing;
 This is important because the fetus and mother may have different blood groups and
any mixing can result in blood clotting;
 Also the mother’s blood pressure is higher compared to the fetus which might
damage the fetal organs;
 Blood from fetus passes through the umbilical cord in the umbilical artery to the
 Substances that diffuse across the placenta are as follows:
Type of substance
Respiratory gases
Soluble nutrients
Nitrogenous excretory
Potentially harmful
To fetus from mother
Amino acids, glucose, fatty
acids, glycerol, vitamins,
minerals, water
Antibodies, antibiotics
To mother from fetus
Carbon dioxide
Alcohol, nicotine and other
drugs, viruses, bacteria
9. Describe the advantages and disadvantages of breast-feeding compared with bottlefeeding using formula milk.
Advantages of breast-feeding over bottle-feeding:
 There are antibodies present in the breast milk, giving the baby protection against
 Foodstuffs are present in breast milk in the correct proportions;
 There are no additives and preservatives in breast milk;
 Breast feeding builds a bond between mother and baby;
 Breast milk does not require sterilization as there are no bacteria present that could
cause intestinal disease;
 Breastfeeding triggers a reduction in the size of the mother’s uterus.
 Formula milk is much more expensive than breast milk, which is free.
Advantages of bottle-feeding over breast-feeding:
 Someone else can feed the mother’s baby;
 This can also help the father to bond with the baby, if he is involved in feeding.
10. Describe the method of transmission of human immunodeficiency virus (HIV), and
the ways in which HIV/AIDS can be prevented from spreading.
HIV may result in AIDS
Methods of transmission
Unprotected sexual intercourse with an
infected person
Drug use involving sharing a needle
used by an infected person
Transfusions of unscreened blood
Infected mother to fetus
Feeding a baby with milk from an
infected mother
Use of unsterilized surgical instruments
Ways of preventing its spread
Use of condom for sexual intercourse
Abstinence from sexual intercourse
Screening of blood used for transfusions
Use of sterilized needles for drug injections
Feeding a baby with bottled milk when the
mother has HIV
Use of sterilized surgical instruments
11. Outline how HIV affects the immune system in a person with HIV/AIDS.
 HIV virus attacks some types of lymphocyte (white blood cells) in the bloodstream;
 Lymphocytes produce antibodies, which attack the antigens present on invading
 So HIV stops this happening - thus the person develops symptoms of AIDS;
 So they become vulnerable to infections (like pneumonia, tuberculosis and cancer);
 A person with AIDS usually dies of a collection of several illnesses.
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