Reproduction (Edexcel IGCSE Biology)

Sexual reproduction involves two parents while asexual reproduction involves one parent.

Meiosis is required for sexual reproduction.

Fertilisation is the fusion of gamete nuclei, resulting in the formation of a zygote.

Fertilisation in humans involves the fusion of a sperm cell with an egg cell.

The result of fertilisation is the formation of a zygote/fertilised egg cell.

True.

Fertilisation leads to variation in offspring.

A zygote is a fertilised egg cell formed by the fusion of gamete nuclei.

Variation in offspring allows for adaptation to changing environments.

The main source of genetic variation in offspring in sexual reproduction is the production of gametes by meiosis, resulting in new combinations of alleles on the chromosomes.

Fertilisation is important as it leads to the formation of genetically diverse offspring.

False.

Fertilisation involves the fusion of gametes from different parents.

An embryo is the early developmental stage of a multicellular organism that is produced after cell division of a zygote.

Pollination is the process of transferring pollen from the anther (male part) to the stigma (female part) of a flower.

The two main mechanisms of pollination are insect pollination and wind pollination.

False.

Pollen is not capable of locomotion. It requires a mechanism such as wind, water or insects to transfer it from place to place.

Insect-pollinated flowers have structures that allow insects to transfer pollen, such as sticky pollen and nectar-producing glands. They attract insects using brightly coloured petals and attractive smells.

Wind-pollinated flowers produce large amounts of lightweight pollen and have exposed stigmas to catch the pollen carried by the wind.

Cross-pollination occurs when pollen is transferred from the anther of a flower to the stigma of a flower from another plant of the same species.

Self-pollination occurs when pollen is transferred from the anther of a flower to:

• the stigma of the same flower

• the stigma of another flower on the same plant

Pollination is crucial for plant reproduction as it facilitates the transfer of pollen, leading to fertilisation and the production of seeds and fruits.

True.

Petals of insect-pollinated flowers tend to be brightly coloured to attract pollinator insects.

Anthers are adapted in wind-pollinated plants by swinging on long filaments outside of the flower to transfer pollen to the wind.

Fertilisation is the process in which the nucleus of a male pollen grain fuses with the nucleus of an ovum in the ovary, leading to the formation of a zygote.

Fertilisation in plants occurs when the pollen grain nucleus fuses with the ovum nucleus, typically in the ovary.

False.

The ovule contains the ovum, which is the female gamete.

The pollen tube grows from the pollen grain towards the ovary, allowing the pollen nucleus to reach the ovum for fertilisation.

After fertilisation, the ovule develops into the seed, while the ovary forms the fruit.

Fertilisation is essential for plant reproduction as it leads to the formation of a zygote, which develops into an embryo plant within the seed.

True.

Fertilisation occurs when the nucleus of a male pollen grain fuses with the nucleus of the ovum (gametes) in the ovary.

After fertilisation, the zygote develops into an embryo plant.

An ovule is a structure within the ovary of a flower that contains the ovum, which is the female gamete.

After fertilisation, the ovule develops into the seed, while the ovary forms the fruit.

Germination is the start of growth in a seed under suitable conditions of water, oxygen, and warmth. It is characterised by:

• The swelling of the seed

• Bursting of the seed coat

• The emergence of the embryo plant

The three factors required for successful germination are:

• Water

• Oxygen

• Warmth

False.

Carbon dioxide is not necessary for germination, but its presence does not inhibit the process either.

The control tube contains all the factors required for germination and serves as a baseline for comparison with the other tubes where one of the factors is selectively removed.

The oil layer prevents oxygen from reaching the seeds, selectively removing the oxygen factor to observe its effect on germination.

False.

Germination cannot occur if any one of the three required factors (water, oxygen, warmth) is absent.

Repeating the experiment ensures that the results obtained are reliable, reducing the impact of random errors and anomalous results when calculating a mean.

The independent variable is the abiotic conditions in which the seeds are germinating.

This is part of the CORMMS criteria for planning an investigation.

The dependent variable is how many seeds in each abiotic condition germinate.

This is part of the CORMMS criteria for planning an investigation.

Two control variables in the germination experiment are:

• Temperature (for tubes where the temperature is not being investigated as an abiotic factor)

• Type of water used (i.e. sterile water)

This is part of the CORMMS criteria for planning an investigation.

The organism being investigated in the germination experiment is the same species of seeds.

This is part of the CORMMS criteria for planning an investigation.

True.

Germination is the start of growth in a seed, leading to the emergence of the embryo plant.

Cotyledons are seed leaves that surround and protect the embryo within the seed.

The role of cotyledons during germination is to provide food reserves to the developing seedling until it can photosynthesise and produce its own food.

During germination, the seed absorbs water, causing the seed coat to split. The embryo plant then grows, with the emergence of the plumule (shoot) and radicle (root).

Cotyledons store food reserves that provide nourishment to the developing seedling until it can produce its own food through photosynthesis. They supply the energy required for growth during the early stages of germination.

During germination, the plumule (first shoot) and radicle (first root) emerge from the seed.

The plumule develops into the shoot system, while the radicle grows into the root system.

True.

Cotyledons are part of the embryo plant contained within the seed, providing nourishment and support during the early stages of growth.

Water is essential for germination as it triggers the activation of enzymes within the seed, leading to the breakdown of stored nutrients.

It also causes the seed coat to split, allowing the embryo plant to emerge and initiate growth.

The seed coat protects the embryo plant within the seed and regulates the entry of water. During germination, it splits open to allow the emerging plumule and radicle to grow and initiate the development of the seedling.

Asexual reproduction in plants involves the production of offspring from a single parent, resulting in genetically identical offspring, known as clones.

False.

Asexual reproduction in plants results in genetically identical offspring, which are exact copies of the parent plant.

Natural asexual reproduction in plants involves the growth of side branches called runners, which produce small plantlets at their ends. These plantlets develop roots upon touching the soil and eventually become independent plants.

Artificial asexual reproduction in plants involves removing a section of a healthy parent plant with a new bud. This cutting is then placed in water or soil until new roots grow, resulting in a genetically identical offspring, or clone, of the parent plant.

The purpose of taking cuttings is to produce genetically identical plants quickly and cheaply, allowing gardeners to propagate desirable traits from healthy parent plants.

False.

Artificial asexual reproduction in plants is a process controlled by humans, involving techniques such as taking cuttings to propagate desirable traits from parent plants.

Runners develop roots upon touching the soil, eventually becoming independent plants that are genetically identical to the parent plant.

Rooting powder contains plant growth regulators/rooting hormones, that stimulate the growth of new roots on plant cuttings.

Natural asexual reproduction occurs without human intervention (such as through runners) while artificial asexual reproduction involves human-controlled methods (such as taking cuttings) to propagate desirable traits from parent plants.

The offspring produced through asexual reproduction are known as clones, which are genetically identical to the parent plant.

True.

The male reproductive system consists of several structures, the male reproductive system includes the penis, testes, and urethra among others.

The testes are responsible for the production of sperm cells. They also secrete the hormone testosterone, essential for the development of male reproductive organs and secondary sexual characteristics.

True.

The prostate gland produces a milky fluid that contributes to semen volume. This fluid contains enzymes and nutrients that support sperm motility, as well as substances that help neutralise the acidity of the female reproductive tract.

The male reproductive system produces and delivers sperm cells to the female reproductive system during sexual intercourse.

The sperm duct delivers sperm cells to the urethra where it is mixed with fluids/semen before being passed out of the penis during ejaculation.

The ovary is part of the female reproductive system which contains ova (egg cells) ready to mature and be released during ovulation.

The cervix is a ring of muscle at the entrance of the uterus. It keeps the developing fetus inside the uterus during pregnancy. It expands (dilates) during birth to allow passage of the baby through the vagina.

The oviduct is a tube connecting an ovary to the uterus. It is lined with ciliated cells which help deliver a mature ovum (egg cell) from the ovary to the uterus. Fertilisation of the ovum by a sperm cell occurs in the oviduct.

The uterus is a muscular bag where a fertilised ovum is implanted which will develop into a fetus during pregnancy.

True.

The vagina is a muscular tube where a man's penis is inserted during sexual intercourse. It leads to the woman's uterus.

The menstrual cycle is the sequence of events that includes the thickening of the uterus lining, ovulation and menstruation; it is controlled by a series of hormones.

Oestrogen causes the uterus lining to thicken during the first part of the menstrual cycle. It also interacts with other hormones to bring about maturation of an egg cell.

Oestrogen levels rise from day 1 and peak just before day 14. The peak in oestrogen occurs just before the egg cell is released.

False.

A decrease in progesterone levels at the end of the cycle results in the loss of the lining during menstruation.

Progesterone levels are low from day 1 – 14 and starts to rise once ovulation has occurred. Levels then decrease towards the end of the cycle.

FSH is released by the pituitary gland and causes an egg to start maturing in the ovary. It also stimulates the ovaries to start releasing oestrogen.

When oestrogen levels reach their peak the pituitary gland is stimulated to release LH (luteinising hormone).

False.

LH causes ovulation to occur. It is FSH that causes an egg cell to begin to mature.

The fetus gains the following substances from the mother's blood:

• Glucose

• Amino acids

• Fatty acids

• Water

• Oxygen

• Mineral ions

• Vitamins

False.

The mother's blood and that of the fetus are separated by a membrane within the placenta.

Substances are exchanged between the mother's blood and the fetus' blood in the placenta. Here substances cross the placental membrane by diffusion.

The mother's blood receives the following waste products from the fetus at the placenta:

• Carbon dioxide

• Urea

The movement of most molecules across the placenta occurs by diffusion. For some substances active transport may be involved.

The placenta is adapted for diffusion by:

• Large surface area of contact between the mother's blood and that of the fetus

• A short diffusion distance between the mother's blood and the fetus' blood

Embryo development occurs in the uterus after the embryo has implanted into the uterus lining.

The role of the amniotic fluid is to protect the developing embryo from being bumped by the movements of the mother's body.

Secondary sexual characteristics are features that are not present at birth but that develop during puberty.

The two hormones that control the development of secondary sexual characteristics are:

• Oestrogen (females)

• Testosterone (males)

Examples of secondary sexual characteristics that develop in females include:

• Breasts develop

• Body hair grows

• Widening of hips

• Menstruation begins

• Growth of sex organs

False.

The secondary sexual characteristics in males develop in response to the hormone testosterone. Oestrogen is involved with stimulating development of secondary sexual characteristics in females.