16 Reproduction

Question 1

Asexual reproduction

Answer 1

A process resulting in the production of genetically identical offspring from one parent.

Organisms that can reproduce asexually include:
Bacteria
the starfish
yeast (a single-celled fungus)
many plants such as ferns and the strawberry plant

Question 2

Advantages and disadvantages of asexual reproduction

Answer 2

Advantages
The population can be increased rapidly when conditions are right
Can exploit suitable environments quickly
More time and energy-efficient
Reproduction is completed much faster than sexual reproduction

Disadvantages
Limited genetic variation in population - offspring are genetically identical to their parents
The population is vulnerable to changes in conditions and may only be suited for one habitat
Disease is likely to affect the whole population as there is no genetic variation

Question 3

Sexual reproduction

Answer 3

A process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote, and the production of offspring that are genetically different from each other.

Question 4

Fusion

Answer 4

The process of joining or fusing together two nuclei during sexual reproduction.

Question 5

Fertilisation

Answer 5

The fusion of gamete nuclei to form a zygote.

Question 6

Zygote

Answer 6

A cell produced by the fusion of the nuclei from two gametes during fertilisation. The nucleus of a zygote is diploid – it contains two sets of chromosomes.

Question 7

Halpoid

Answer 7

Describes a nucleus containing a single set of unpaired chromosomes.

Question 8

Diploid

Answer 8

Describes a nucleus containing two sets of chromosomes, for example in body cells.

Question 9

Advantages and disadvantages of sexual reproduction

Answer 9

Advantages
Increases genetic variation Takes time and energy to find mates
The species can adapt to new environments due to variation, giving them a survival advantage
Disease is less likely to affect the population (due to variation)

Disadvantages
Difficult for isolated members of the species to reproduce
Takes time and energy to find mates

Question 10

Pollination

Answer 10

The transfer of pollen grains from the anther to the stigma.

Question 11

Flower male parts

Answer 11

Sepal: green part at the top of the stem, underneath the petals. To protect the growing flower and help to stop it drying out

Petal: brightly coloured part of the flower to attract insects, birds or mammals to carry out pollination

Stamen: the male part of the flower consisting of the filament and the anther. To produce male gametes (pollen) and provide the correct structures and conditions necessary for the transfer of pollen

Filament: the stalk that supports the anther. To hold the anther in a position where it is able to transfer its pollen to an insect, mammal or bird

Anther: coloured, usually with a powdery appearance to produce pollen grains, which contain the plant’s male gametes

Question 12

Flower female parts

Answer 12

Stigma:usually green and the tallest part of the inside of the flower, and with a sticky, waxy layer to trap pollen from other flowers

Style: the thin structure that supports the stigma and is above the ovary,to support and present the stigma in a position where it can receive pollen from an insect, bird or mammal

Carpel: the female part of the flower that contains the stigma, style and ovary to produce female gametes and provide the correct structures and conditions necessary for fertilisation

Ovary: green, bulb-shaped part near the bottom of the flower, contains ovules (which contain the female gametes) which will develop into seeds after fertilisation

Ovule: structures within the ovary, female gametes are produced and contained within the ovules. Upon fertilisation, these ovules will develop into seeds

Question 13

Pollen for insects and for wind

Answer 13

Insects:
The spiky outer layer hooks onto insects so that the pollen can be transported from one flower to another

Wind:
Pollen that is transported by the wind is smaller, lighter and smoother. This allows the pollen grains to be blown from one flower to another.

Plants produce millions of pollen grains, but wind-pollinated flowers tend to produce much more pollen than insect-pollinated flowers. This increases the chance of wind-blown pollen reaching another plant from the same species.

Question 14

Self and cross-pollination

Answer 14

Self
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
Transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.

Question 15

Structure of flower wind, insect

Answer 15

Wind-pollinated flower:
Petal: small and usually dull in colour because they do not need to attract insects
Anther: loosely attached and dangle outside the flower so its pollen can be blown easily by the wind
Stigma: loosely attached and dangle outside the flower so they can catch wind-borne pollen from other plants; often appear feathery

Insect-pollinated flower
Petal: large and brightly coloured to attract insect pollinators
Anther: located inside the flower to brush against insects
Stigma: located inside the flower to brush against insects
Nectar to attract insects

Question 16

Fertilisation in plant

Answer 16

Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule
After pollination, a pollen tube begins to grow through the style towards the ovary.
Two male gametes, the sperm, move through this tube. Eventually the pollen tube reaches the ovule. The nucleus of one of the two sperm cells fuses with the egg cell (female gamete) nucleus (fertilisation) to form a zygote .
The zygote develops into an embryo, which eventually becomes the new plant.

Question 17

Germination

Answer 17

The process, controlled by enzymes, in which the seed begins to develop into a new young plant.

To germinate, most seeds need:
water
oxygen
a suitable temperature.

Question 18

Male reproduction system

Answer 18

Testis: organ in which sperm cells and testosterone are produced
Scrotum: sack of skin that contains the testes, helping to keep them at a slightly lower temperature than the rest of the body
Prostate gland: secretes fluid that nourishes and protects the sperm; the mixture of liquid and sperm is known as semen
Sperm duct: muscular tube that connects a testis to the urethra
Urethra: tube that allows the passage of semen and urine through the centre of the penis
Penis: during sexual intercourse, the penis is inserted into the vagina, allowing the sperm to transfer into the female reproductive system

Question 19

Female reproductive system

Answer 19

Ovary: produces egg cells, and the hormones oestrogen and progesterone
Oviduct: tube connecting an ovary to the uterus; fertilisation usually occurs here
Uterus: organ in which the embryo develops
Cervix: ring of muscle between the vagina and the uterus
Vagina: elastic muscular canal through which the newborn passes during childbirth; during sexual intercourse, the male’s penis is inserted into the vagina

Question 20

Sperm cells

Answer 20

The tip of the head has a structure called the acrosome. This secretes digestive enzymes that allow the sperm cell to pass through the jelly coating on the surface of an egg cell.

The flagellum is the part of the sperm cell that can move, rather like a tail, propelling the cell from one place to another.

The midpiece of the sperm cell contains many mitochondria. These organelles release energy by respiration, which is needed to keep the flagellum moving.

Question 21

Egg cell

Answer 21

The nucleus contains the mother’s DNA that will fuse with the father’s contained in the sperm’s nucleus.

The cytoplasm contains energy stores to allow the egg to survive for several days and nourish the zygote if fertilisation occurs until it can implant in the uterus wall.

The jelly coat around the egg cell allows the sperm to attach and creates a barrier to other sperm cells once one has successfully penetrated it and entered the egg cell.

The layer of follicle cells attached to the egg helps to nourish the egg during its journey.

Question 22

SEX

Answer 22

During sexual intercourse for reproduction, a man places his erect penis into a woman’s vagina.

Eventually, semen leaves the penis during ejaculation and enters the vagina.

Sperm in the semen then attempt to swim up the vagina, through the cervix, into the uterus and along the oviducts.

However, the majority of the sperm will not survive the journey.

A few may make it far enough to come into contact with the egg, but only one will be able to fertilise it as, once the first sperm is successful, a barrier is formed to prevent any more from entering.

Fertilisation is the fusion of the nucleus from a male gamete (sperm) and the nucleus from a female gamete (egg cell) to form a zygote.
Sperm cells and egg cells are adapted to their functions.

Question 23

Embryo

Answer 23

A ball of cells produced by the cell division of a zygote.

Question 24

Pregnancy

Answer 24

In early development, the zygote forms a ball of cells called an embryo
Fertilisation and development of the zygote into an embryo.
Around five days after fertilisation, the embryo implants into the wall of the uterus, where it continues to divide and grow.

Question 25

The fetus

Answer 25

Name for an embryo after (8 weeks in humans).

In the early stages, the complexity of the fetus increases as its cells become specialised, and its tissues, organs and organ systems form. Its size increases considerably towards the end of the pregnancy.

The fetus is surrounded by a protective layer called the amniotic sac, which is filled with amniotic fluid. The amniotic fluid also contains nutrients needed by the fetus. It also helps to protect the fetus.

Question 26

Placenta

Answer 26

A structure called the placenta grows inside the mother, attached to the wall of her uterus.
The placenta has two main functions:

It transfers substances from the mother to the fetus.
It transfers waste substances from the fetus to the mother so her body can excrete them.

Question 27

Umbilical cord

Answer 27

A cord which connects the fetus to the placenta and contains blood vessels which transport nutrients, oxygen and waste products.

Question 28

Exchange of materials during pregnancy

Answer 28

The placenta provides the fetus with the oxygen, carbohydrates, proteins, fats, vitamins, minerals and water it needs to grow.
As it grows, the fetus produces waste products, mainly carbon dioxide and urea.
The blood supply of the mother does not meet the blood supply of the fetus.
Instead, substances diffuse through blood capillaries between the placenta and umbilical cord

Question 29

Toxins transmitted during pregnancy

Answer 29

Nicotine (for example, from tobacco smoke)
some pathogens (for example, the rubella virus).

Question 30

Puberty

Answer 30

The life stage during which bodies change physically and they become able to reproduce.

Question 31

Testosterone and oestrogen

Answer 31

The main male sex hormone. It plays a key role in the primary and secondary sexual systems in males.
The main female sex hormone. It plays a major role in the control of the menstrual cycle

Question 32

secondary sexual characteristics

Answer 32

more hair on the limbs and torso
the growth of pubic hair.

In Males:
facial hair grows
the voice box (the ‘Adam’s apple’) becomes larger
the voice ‘breaks’ and becomes deeper
shoulders and chest widen and muscle mass increases.

In females:
breasts enlarge
hips widen.

Question 33

Mensural cycle

Answer 33

The menstrual cycle is a normal process most individuals with female sex organs experience, beginning during puberty. There are changes to the ovaries and the lining of the uterus in the body during the menstrual cycle.

Question 34

Ovaries

Answer 34

The ovaries release an egg cell about once every month (28 days)(varies by 21-40)
In the ovaries, egg cells develop within structures called follicles.
Once mature, the egg is released from the follicle.
This process is called ovulation.
It happens in the middle of the cycle, usually around day 14
After ovulation, the follicle develops into a structure called the corpus luteum.

Question 35

The lining of the uterus

Answer 35

From day 4 of the menstrual cycle, the lining of the uterus thickens.

This is so that the egg cell can implant into the lining if the egg is fertilised by a sperm cell.

If the egg is not fertilised, the lining of the uterus will break down again.

It will be discharged from the body through the vagina during menstruation.

The discharge of menstrual fluid (blood and other material from the lining of the uterus) is often called a period and marks the beginning of the next cycle.

A period can last from just a few days to around a week.

Question 36

Four hormones are involved in the control of the menstrual cycle and pregnancy:

Answer 36

FSH: causes an egg in an ovary to mature, stimulates the ovary to secrete oestrogen

LH: stimulates the release of a mature egg

oestrogen: inhibits the release of FSH, stimulates the release of LH

progesterone: involved in maintaining the lining of the uterus, inhibits the release of FSH and LH

Question 37

Pregnancy development

Answer 37

If a woman becomes pregnant, the corpus luteum continues to release oestrogen and progesterone. At around 8–12 weeks of pregnancy, the placenta takes over the production of these hormones.
This will:
Ensure that no more eggs are released from the ovaries
Maintain a thick uterine lining to support the growing fetus
Prevent the muscles of the uterus contracting, which would cause the early delivery of a premature baby.

Question 38

Sexually transmitted disease

Answer 38

An infection that is transmitted via body fluids through sexual contact.

virus: genital warts, herpes, HIV
bacterium: chlamydia, gonorrhoea, syphilis

Question 39

HIV/AIDS

Answer 39

The human immunodeficiency virus (HIV) is an example of a sexually transmitted infection. Infection with HIV can lead to AIDS (acquired immune deficiency syndrome).

HIV can only be transmitted by direct contact with certain body fluids from an infected person who has a detectable viral load (the amount of the virus in their blood).
These fluids include blood, semen and vaginal fluid. They must get into the blood for infection to occur, for example through unprotected sex, cuts and sores, using contaminated needles for injecting drugs or when receiving blood transfusions.

HIV can also be transmitted from mother to child during childbirth, pregnancy and through breast-feeding.