D3.1 Reproduction

Question 1

What are features of asexual reproduction?

Answer 1

• Requires only one parents
• Reproduces through mitosis throughout an asexual life cycle
• All genes are passed onto offspring
• Offspring is genetically identical to each other and parent
• No genetic variation (minor caused by mutation)
• Better adapted to an unchanging environment

Question 2

Advantages of asexual reproduction?

Answer 2

• No need to locate a mating partner
• Large number of offspring created
• If conditions are optimal, all individuals are perfectly well adapted

Question 3

What are features of sexual reproduction?

Answer 3

• Requires two parents
• Reproduces through meiosis once per generation in a sexual life cycle
• Each parent passes half of their genes to their offspring
• Offspring are genetically different and has a unique combination of genes from both parents
• Greater genetic variation
• Offspring better adapted than parents if the environment is changing

Question 4

Advantages of sexual reproduction

Answer 4

• Offspring are better adapted to changing conditions due to genetic recombination
• Offspring is widely dispersed

Question 5

Disadvantages of sexual reproduction

Answer 5

• Requires mating partner
• Sexual products usually small
• Often occurs seasonally
• More time needs to be invested in parental care

Question 6

What is the role of meiosis and fusion of gametes?

Answer 6

During meiosis, chromosomes of gametes are halved as parental combinations of genes are broken up, allowing new combinations to form when gametes fuse (fertilization)

Question 7

What are characteristics of male gametes?

Answer 7

• Travels to the female gamete
• Smaller in size
• Has less food reserve, only enough for the gamete
• Produced often in very large numbers

Question 8

What are characteristics of female gametes?

Answer 8

• Sessile
• Larger in size
• More food reserve, enough for the development of an embryo
• Less produced in one time, often only one

Question 9

Draw and label the male reproductive system

Answer 9

1. Testis: produces sperm and testosterone
2. Epididymis: stores sperm until ejaculation
3. Sperm duct: transfers sperm from epididymis to urethra during ejaculation
4. Seminal vesicle & prostate gland: secrete fluid containing alkali, proteins and fructose which is added to sperm to make semen.
5. Urethra: transfers semen during ejaculation and urine during urination.
6. Penis: penetrates the vagina for ejaculation of semen near the cervix
7. Scrotum: holds the testes at a lower than core body temperature.

Question 10

Draw and label the female reproductive system

Answer 10

1. Ovary: produces eggs, estradiol and progesterone
2. Oviduct: collects eggs at ovulation; provides a site for fertilization then moves embryo to uterus
3. Uterus: provides for the needs of the embryo and then fetus during pregnancy,
4. Vagina: stimulates penis to cause ejaculation and provides a birth canal.
5. Cervix: protects the foetus during pregnancy and then dilates to provide a birth canal.
6. Vulva: protects internal parts of the female reproductive system.

Question 11

Explain the menstrual cycle

Answer 11

1. In the beginning of the follicular phase, the PG secretes FSH, stimulating the development of follicles in the ovary.
2. At the end of the follicular phase, the developed follicle secretes estradiol, stimulating the endometrium’s thickening. This leads to an increase in FSH receptors on the follicles, boosting estradiol production (positive feedback)
3. In the beginning of the luteal phase, when estradiol reaches its highest level, further secretion of FSH is inhibited, preventing any more follicles from developing (negative feedback).
4. LH is then secreted by the PG, triggering ovulation, where the most developed follicle breaks open, releasing a mature egg into the oviduct. The secretion of LH also promotes the conversion of the follicle wall into a corpus luteum.
5. Corpus luteum secretes progesterone and to a lesser extent, estradiol. Progesterone maintains the thickening of the endometrium. Further secretion of LH and FSH in inhibited.
6. If there is no fertilization: At the end of the L phase, the rapid decrease of FSH and LH in the bloodstream causes the corpus luteum to break down, causing levels to progesterone and estradiol to fall. This causes the endometrium to break down, beginning menstruation and another cycle. Falling levels of progesterone stimulates the PG to secrete FSH.

– If there is fertilization: The developing embryo becomes an endocrine gland, secreting a hormone that circulates in the blood and maintains the corpus luteum (positive feedback). When the corpus luteum eventually breaks down, the placenta takes over as an endocrine gland, secreting estradiol and progesterone, preventing ovulation and maintaining the endometrium (negative feedback).

Question 12

What is fertilization?

Answer 12

The fusion of a sperm with an egg to form a zygote

Question 13

Explain the process of fertilization

Answer 13

1. Receptors on the plasma membranes of sperm cells detects chemicals released by the egg, allowing directional swimming of the sperm to reach the egg.
2. Many sperm will push between the follicle cells to reach the zona pellucida, a layer of glycoproteins.
3. The acrosome of sperm cells contains enzymes that digest the egg cell’s glycoproteins to reach the egg’s plasma membrane.
4. The first sperm cell that manages to penetrate the zona pellucida will bind to the plasma membrane of the egg.
5. The nucleus of this sperm cell enters the egg cell and will fuse together with the nucleus of the egg cell. Every other part of the sperm cell is broken down.
6. The layer of glycoprotein around the egg reforms, preventing further sperm from entering. This ensures that a diploid zygote is produced, rather than an unviable cell with more than two sets of chromosomes.

Question 14

How does In-vitro fertilization happen?

Answer 14

1. Menstruation cycle is prevented by injecting a drug to stop the secretion of FSH and LH, allowing doctors to control the ovarian and uterine cycle.
2. Synthetic FSH is injected to stimulate many follicles to develop. The follicles are then stimulated to mature by the injection of the hormone hCG.
3. Several eggs are drawn out of the follicles in the uterus using a laparoscope with the aid of a ultrasound scanner.
4. Eggs are mixed with sperm cells in a shallow dish. If fertilisation happens, one or more embryos are placed in the uterus and may implant.

Question 15

What are the male sex organs in a plant?

Answer 15

Anther and filament which makes up the stamen
- Anther: one diploid cell divides by meiosis to produce 4 haploid pollen grains. the nucleus in each of these divides again by mitosis to produce 3 haploid nuclei, two of which are male gametes.
- Filament: holds the anther in an elevated position

Question 16

What are the female sex organs in a plant?

Answer 16

Stigma, style, and ovary which makes up carpel
- Stigma: receives pollen grains
- Style: connects stigma to ovary
- Ovary: ontains one or more ovules that divides by meiosis to produce 4 haploid cells, which then divides by mitosis to produce 8 haploid nuclei, one which is the female gamete or egg.

Question 17

Define pollination

Answer 17

The transfer of pollen from one stigma to another, usually moved by wind or by animals

Question 18

How does pollination occur?

Answer 18

Fertilization takes place inside an ovule, in the ovary.

1. A pollen grain that lands on a stigma forms a pollen tube growing from the style down to the ovary which carries the male gametes.
2. When the pollen tube reaches the center of the ovule where the female gamete is located, the male gametes are released and fertilization occurs.
3. A zygote is formed, which develops into an embryo with an embryo root, an embryo shoot, and either one or two embryo leaves.

Question 19

Features of an insect-pollinated flower

Answer 19

• Large, brightly colored petals acting as a landing stage and guides the insect’s movements to the anther or stigma
• Scent is secreted from the petals to attract insects
• Large and spiky pollen grains that are attractive and stick to insects
• Stigma is large and sticky to collect pollen from insects
• Nectaries secrete nectar to attract insects
• Nectaries positioned deep inside the flower so insects can only reach them by brushing past the anthers and stigma

Question 20

What are methods of cross-pollination? (hint: to make self-pollination less likely)

Answer 20

1. adaptations to facilitate transfer of pollen from one plant to another by an outside agent.
2. separation of anthers and stigmas/styles/ovaries in separate male and female flowers on the same or different plants.
3. anthers and stigmas maturing at different time.

Question 21

What are the self-incompatibility mechanisms?

Answer 21

• Despite features of flowering that reduce the chance of self-pollination, self-pollination will happen when a stigma of a hermaphrodite plant receives pollen from that plant’s own stamens.
• However, due to self-incompatibility, this pollen will fail to germinate or stops growing before reaching the ovaries, preventing inbreeding.

Question 22

Outline the process of seed germination

Answer 22

1. The radicle emerges first, anchoring the seedling in the soil water and absorbs water and mineral ions.
2. The young embryo stem emerges as the seed coat is split away from the cotyledons. The hooked shoot protects the young leaves from damage by soil particles.
3. The stem grows upwards retaining its hooked shape.
4. Foliage leaves show. The shoot (plumule) emerges above ground and starts to straighten out to lift foliage leaves above the soil.

Question 23

What are the conditions necessary for germination to occur?

Answer 23

• Warmth as germination involves enzyme catalysed metabolic reactions
• Water for rehydration
• Oxygen for aerobic cell respiration and energy production
• Plant hormones (e.g. gibberelin) stimulates mitosis and cell division in the embryo and the production of amylase in starchy seeds.