Reproduction (Edexcel IGCSE Science (Double Award): Biology): Flashcards

Offspring produced by asexual reproduction are genetically identical, so they are called clones.

Gametes are produced by meiosis, which halves the chromosome number.

False.

Asexual reproduction needs no gametes and no fertilisation — only one parent cell is required.

True.

Asexual reproduction is common in plants.

A sex cell produced by meiosis, containing half the number of chromosomes of a normal body cell.

• Animals — the sperm and the ovum

• Plants — the pollen nucleus and the ovum

23 — half the number in a normal body cell.

• A tail to propel it towards the egg

• Mitochondria to provide the energy for that movement

It has energy stores in its cytoplasm to support early embryo development.

The fusion of a male gamete and a female gamete to produce a zygote.

It divides by mitosis to develop into an embryo, which grows into the new offspring.

In the oviduct, typically 1–2 days after ovulation, if a sperm meets an egg.

46 — 23 pairs. Half come from the father and half from the mother.

A pollen tube grows down from a pollen grain to deliver the male nucleus into the ovary, where the male and female gametes fuse to form the embryo.

The fusion of a male and female gamete produces a zygote.

In humans, fertilisation takes place in the oviduct.

False.

Gametes contain half the number — 23 in humans, compared with 46 in a normal body cell.

False.

A zygote divides by mitosis. It is the gametes that are produced by meiosis.

The transfer of pollen from the male part of a flower to the female part of a flower.

• Male — in the pollen grains

• Female — in the ovules

It protects the unopened flower.

• Anther — produces and releases pollen

• Filament — provides support to the anther

• Stigma — the sticky top of the female part, which collects pollen grains

• Style — a tube connecting the stigma to the ovary

• Ovary — contains the ovules

• Ovule — the structure inside the ovary containing the female gametes

• Large, brightly coloured petals to attract insects

• Scent and nectar to encourage insects in past the stamen

• Anthers on stiff filaments inside the flower, so they brush against insects

• Sticky stigmas inside the flower to catch pollen as insects brush past

As the insect enters a flower for nectar, it brushes against the anthers, which deposit sticky pollen on its body.

At the next flower it brushes against the stigma and deposits some of that pollen.

• Small, dull petals, often green or brown — colour would waste energy

• No scent or nectar, which would also waste energy

• Anthers on long filaments outside the flower, to release pollen into the wind

• Feathery stigmas outside the flower, to catch airborne pollen

So that pollen can easily be blown away by the wind, and easily be caught by the stigmas of other flowers.

Because they do not need to attract insects, so producing nectar would be a waste of energy.

Wind-pollinated flowers have feathery stigmas that hang outside the flower to catch airborne pollen.

The anther produces and releases pollen grains.

True.

Sticky pollen clings to the insect's body, so it is carried to the next flower.

False.

Their petals are small and dull, often green or brown — bright petals would waste energy since no insects need attracting.

A pollen tube, which grows down the style towards the ovary to deliver the male nucleus to the ovum.

The pollen nucleus and the ovum nucleus fuse together to form a zygote.

• Pollination — pollen landing on the stigma of a flower

• Fertilisation — the fusion of the male and female nuclei

A seed.

A fruit, which contains the seeds.

It provides a mechanism for seed dispersal.

• Some fruits are eaten by animals, which disperse the seeds in their droppings

• Some fruits have sticky hooks that catch in the fur of passing animals

The style, on its way from the stigma to the ovary.

After pollination, a pollen tube grows down the style to deliver the male nucleus to the ovum.

After fertilisation the ovule develops into a seed.

False.

Pollination is pollen landing on the stigma. Fertilisation is the later fusion of the male and female nuclei.

False.

The ovule becomes the seed. The fruit develops from the parts of the flower surrounding the ovule.

• Water

• Oxygen

• Warmth

It swells the seed, breaks the seed coat, and activates the enzymes needed for growth.

It is necessary for respiration, which provides the energy for growth.

It increases enzyme activity, improving germination up to a certain temperature.

Put 10 cress seeds on cotton wool in each of four labelled tubes.

A — cotton wool kept dry.

B — cotton wool moistened (the control).

C — seeds covered with water plus a layer of oil on top.

D — cotton wool moistened, tube placed in a fridge at 4 °C.

Keep A, B and C at about 20 °C and compare after 3–5 days.

• A — water is absent

• B — the control, all factors present

• C — oxygen is blocked

• D — warmth is removed

The oil and water layers block oxygen from reaching the seeds.

Only tube B, the control.

Germination requires all three factors, and B is the only tube where none has been removed.

The temperature of tubes A, B and C, and the type of water used — sterile water, made by boiling then cooling it.

So that the seeds are as similar as possible, and any difference in germination is due to the conditions, not the seeds.

Tube D is placed in a fridge at 4 °C to remove warmth from the seeds.

Water activates the enzymes inside a seed that are needed for growth.

False.

Without water the seed coat cannot break and the enzymes are not activated, so no germination occurs.

True.

Removing any one of water, oxygen or warmth prevents germination — which is why only the control tube succeeds.

• An embryo shoot

• An embryo root

• Seed leaves, known as cotyledons

• A food store, containing starch and other nutrients

A seed leaf — part of the seed that contains the plant's early food store.

Enzymes break the stored starch down into maltose and then glucose.

The glucose is used in respiration to release energy for the growth of the shoot and root.

Once larger leaves emerge, so that photosynthesis can begin and the plant can make its own food.

Starch and other nutrients.

Because starch is a large, insoluble molecule. It must be broken into glucose before it can be used in respiration.

It begins to grow, using up the food reserves from the seed's food store.

Enzymes in a germinating seed break stored starch down into maltose and then glucose.

The seed leaves inside a seed are called cotyledons.

False.

It relies on its food store until larger leaves emerge, at which point photosynthesis can begin.

True.

Respiration releases the energy needed for the shoot and root to grow.

Nutrients and energy, until it can make its own food by photosynthesis.

Only one parent is involved, so all the offspring are exact genetic copies of each other and of the parent plant.

A horizontal stem that grows sideways out of a parent plant, carrying small plantlets at its end.

Once the plantlets at the end of a runner touch the soil, they grow roots, then grow on and become independent of the parent plant.

Natural asexual reproduction. Cuttings are the artificial method.

Choose a healthy parent plant and cut off a section carrying a new bud.

Place the cutting in water until new roots grow, or sometimes directly into soil.

Then plant it and let it grow into an adult plant.

A powder containing plant growth regulators (rooting hormones).

Dipping the cutting's stem into it encourages new root growth.

Because the new plants are genetically identical to the parent, so they will share its desirable characteristics.

New plants can be produced cheaply and quickly.

Plants reproduce asexually in nature using runners, horizontal stems that grow sideways.

The stem of a cutting may be dipped in rooting powder to encourage new roots to grow.

True.

Taking cuttings is a form of asexual reproduction, so the new plant is a clone.

False.

Plants can reproduce both asexually and sexually.

It produces sperm (the male gamete) and the hormone testosterone.

It is contained in a bag of skin called the scrotum.

To keep the sperm at a temperature slightly lower than body temperature.

Sperm pass through it to be mixed with fluids produced by the glands, before entering the urethra for ejaculation.

A tube running down the centre of the penis that can carry urine or semen.

A ring of muscle prevents the two from mixing.

It passes urine out of the body from the bladder, and allows semen to pass into the vagina during sexual intercourse.

They contain the ova (female gametes), which mature and develop when hormones are released.

It connects the ovary to the uterus, and is where fertilisation occurs.

It is lined with ciliated cells that push the released ovum along.

A muscular sac with a soft lining, where the embryo implants and develops into a foetus.

A ring of muscle at the lower end of the uterus that keeps the developing foetus in place during pregnancy.

A muscular tube leading into the body, where the penis enters and sperm are deposited during intercourse.

The oviduct is lined with ciliated cells that push the released ovum along.

The testes are held outside the body in a sac of skin called the scrotum.

False.

Fertilisation occurs in the oviduct. The embryo then implants in the uterus.

True.

A ring of muscle in the urethra stops the two from mixing.

About 28 days, though it varies between individuals.

The release of an egg from an ovary, which then travels along the fallopian tube towards the uterus.

It occurs around day 14 of the cycle.

The breakdown and shedding of the uterine lining (endometrium) through the vagina, when the egg has not been fertilised.

It usually lasts 5–7 days.

They rise from day 1 to peak just before day 14, immediately before the egg is released.

• It causes the uterine wall to start thickening

• It causes the egg to mature

They stay low from day 1 to 14, then rise once ovulation has occurred.

It causes the uterine lining to thicken further, ready for a fertilised egg to implant.

A fall in progesterone levels, which causes the uterine lining to break down.

It thickens again in response to hormones, preparing for the possible implantation of a fertilised egg.

After puberty, usually in early adolescence — around age 11–14.

Ovulation occurs around day 14 of the menstrual cycle.

A fall in progesterone levels causes the uterine lining to break down.

True.

Oestrogen rises from day 1 and peaks just before day 14, immediately before the egg is released.

False.

Progesterone stays low from day 1 to 14 and only rises after ovulation.

It divides to form an embryo and travels to the uterus, where it implants in the uterine lining.

To enable the exchange of substances between the mother's blood and the blood of the fetus.

• Oxygen

• Nutrients — glucose, amino acids, vitamins and mineral ions

• Antibodies

• Carbon dioxide

• Urea

No. They come into very close proximity in the placenta, but the two blood supplies never mix.

It connects the fetus's blood supply to the placenta.

• It has a large surface area

• It has a thin wall, for efficient diffusion

• Glucose for respiration, to release the energy needed for growth

• Amino acids to build the proteins it needs to make new tissue

Diffusion, down the concentration gradient between the mother's blood and the blood of the fetus.

At the implantation site, where the embryo embeds in the uterine lining.

The umbilical cord connects the fetus's blood supply to the placenta.

Waste products such as carbon dioxide and urea pass from the fetus to the mother.

False.

Its lungs are not yet in use. Oxygen diffuses from the mother's blood across the placenta.

False.

They come very close so substances can diffuse between them, but the two supplies remain separate.

The fluid that surrounds the developing embryo in the uterus, contained within the amniotic sac.

It protects the embryo or fetus during development, by cushioning it from bumps when the mother moves around.

The amniotic membrane, also known as the amniotic sac.

In the uterus.

Because the mother moves around, and the fluid absorbs the resulting bumps and knocks.

The amniotic sac.

• The amniotic fluid, which protects it physically

• The placenta, which supplies nutrients and oxygen and removes waste

The developing embryo is surrounded by amniotic fluid, which cushions it from bumps.

Amniotic fluid is held inside the amniotic sac.

False.

Its role is physical protection. Nutrients and oxygen are supplied by the placenta.

True.

This is how it protects the embryo and fetus during development.

The embryo, and later the fetus.

The placenta forms at the implantation site in the uterine lining, outside the sac.

The changes that occur during puberty, whose development is controlled by the release of hormones.

Oestrogen.

Testosterone.

• Development of breasts

• Body hair grows

• The menstrual cycle begins

• Hips get wider

• Growth of the penis and testes

• Growth of facial and body hair

• Muscles develop

• The voice breaks

• The testes start to produce sperm

• Growth of the sexual organs

• Growth of body hair

During puberty, when levels of oestrogen in females and testosterone in males rise.

The voice breaks — it deepens.

In females, secondary sexual characteristics are controlled by oestrogen.

Testosterone causes the male voice to break during puberty.

True.

Along with growth of the sexual organs, it is one of the changes common to both.

False.

Oestrogen controls them in females. Testosterone controls them in males.