D3.1 Reproduction

Question 1

Define Reproduction.

Answer 1

Process of generating more members of their own species.
* Sexual reproduction → Change
* Asexual reproduction → Continuity

Question 2

The sexual life cycle in eukaryotic organisms must include two processes: ____ and ____.

Answer 2

Meiosis; Fertilization

Question 3

Describe Fertilization.

Answer 3

• Fusion of male and female gametes.
• Instant when a new individual is formed.
• Usually come from two different parents.
• Therefore, combinations of genes can be generated.

Question 4

Describe Meiosis.

Answer 4

• Occurs during process of creating gametes.
• Gametes are haploid cells (whereas body cells are diploid) and have two copies of most genes.
• Origin of meiosis is unknown.

Question 5

Meiosis and Fertilization.

Answer 5

Fertilization doubles the number of chromosomes each time it occurs. However, the chromosomes are halved during meiosis. Then, parental combinations of genes are broken up, allowing new combinations to form when gametes fuse.

Question 6

Define Isogamy.

Answer 6

The gametes that fuse in many types of fungi are outwardly identical. This is known as isogamy.

Question 7

Define Anisogamous.

Answer 7

Among eukaryotes, there is a trend for the evolution of two distinct types of gamete. All plants and animals are anisogamous, with different male and female gametes.

Question 8

What are the main components of the female reproductive system?

Answer 8

• Ovary
• Oviduct
• Uterus
• Cervix
• Vagina
• Vulva

Question 9

What are the main components of the male reproductive system?

Answer 9

• Testis
• Scrotum
• Epididymis
• Sperm Duct
• Seminal Vesicle and Prostrate Gland
• Urethra
• Penis

Question 10

The menstrual cycle consists of the ____ and ____ together.

Answer 10

Uterine Cycle; Ovarian Cycle

Question 11

The ovarian cycle consists of two halves, the ____ and ____.

Answer 11

Follicular Phase; Luteal Phase

Question 12

What occurs in the follicular phase?

Answer 12

• Group of follicles develops in the ovary.
• In each follicle, an egg stimulated to grow.
• Most developed follicle breaks open.
• This releases egg into oviduct, while other follicles degenerate.
• Release of egg (ovulation), usually occurs on Day 14 of menstrual cycle.

Question 13

What occurs in the luteal phase?

Answer 13

• Wall of follicle that released egg develops into a body called corpus luteum.
• If fertilization doesn’t occur:
  
  • Corpus luteum breaks down.
  • Ovary returns to follicular phase.

Question 14

What occurs in the uterine cycle?

Answer 14

Changes occur to the endometrium (the lining of the uterus) during each menstrual cycle.
* Endometrium becomes thickened, more richly supplied with blood → preparation for implantation of an embryo.
* If no embryo:
* Thickening breaks down towards end of luteal phase.
* Material from it shed during menstruation.
* This day is referred to as a woman’s “period”.
* Once menstruation has ended, usually after 4 to 7 days, the lining of the uterus is repaired and starts to thicken.

Start of period is obvious, so counted as Day 1 of menstrual cycle (when the ovaries return to follicular phase).

Question 15

What are the steps in fertilization?

Answer 15

1. Plasma membranes of sperm have receptors that detect chemicals released by egg. This enables directional swimming to egg.
2. Egg is surrounded by cloud of hair follicles and layer of glycoproteins. Sperm pushes between cells and digests its way through the glycoproteins to reach plasma membrane of egg cell.
3. Sperm’s plasma membrane has proteins that bind to egg cell’s plasma membrane. The first sperm that manages to penetrate the zona pellucida binds and the membranes of sperm and egg fuse together.
4. Sperm nucleus then enters the egg cell. “This is the moment of fertilization.”

Question 16

What are the steps after fertilization?

Answer 16

1. Immediately after fertilization, layer of glycoprotein around the egg hardens to prevent entry of more sperm. This ensures that a diploid zygote is produced, rather than an unviable cell with more than two sets of chromosomes
2. Sperm tail either doesn’t penetrate egg during fertilization or is broken down inside zygote. Sperm mitochondria may also penetrate, but are usually all destroyed.
3. The nuclei from the sperm and egg remain separate until the zygote’s first mitosis.
4. Then both nuclear membranes break down, releasing 23 chromosomes from each nucleus.
5. These chromosomes, half from the mother and half from the father, participate jointly in mitosis using the same spindle of microtubules.
6. Two genetically identical nuclei are produced, each with 46 chromosomes.

Question 17

List the four hormones involved in the menustral cycle.

Answer 17

• Follicle-Stimulating Hormone (FSH)
• Oestradiol
• Luteinizing Hormone (LH)
• Progesterone

Question 18

Describe the follicle-stimulating hormone (FSH).

Answer 18

Protein hormone produced by the pituitary gland. They bind to FSH receptors in the membranes of follicle cells
* Rises to peak near end of menstrual cycle.
* Stimulates development of follicles, each containing an oocyte and follicular fluid.
* Stimulates secretion of oestradiol by the follicle wall.

Question 19

Describe oestradial.

Answer 19

Ovarian steroid hormones, produced by the wall of the follicle and the corpus luteum that develops from it.
* Rises to a peak towards the end of the follicular phase.
* Stimulates the repair and thickening of the endometrium after menstruation and an increase in FSH receptors that make the follicles more receptive to FSH, boosting oestradiol production (positive feedback).
* When it reaches high levels, oestradiol inhibits the secretion of FSH (negative feedback) and stimulates LH secretion.

Question 20

Describe the luteinizing hormone (LH).

Answer 20

Protein hormone produced by the pituitary gland. They bind to LH receptors in the membranes of follicle cells.
* Rises to sudden, sharp peak near end of follicular phase.
* Stimulates completion of meiosis in the oocyte and partial digestion the follicle wall, allowing it to burst open at ovulation.
* Promotes post-ovulation development of follicle wall into corpus luteum.
* Corpus luteum secretes oestradiol (positive feedback) and progesterone.

Question 21

Describe progesterone.

Answer 21

Ovarian steroid hormones, produced by the wall of the follicle and the corpus luteum that develops from it.
* Levels rise at the start of the luteal phase, reach a peak and then drop back to a low level by the end of this phase.
* Promotes the thickening and maintenance of the endometrium.
* Inhibits FSH and LH secretion by the pituitary gland (negative feedback).

Question 22

How does in vitro fertilization occur (IVF)?

Answer 22

1) Downregulation.
2) Intramuscular Injections of FSH
3) Egg Collection
4) Incubation
5) Implantation

See Document for more.

Question 23

List common features of insect-pollinated flowers.

Answer 23

• Large, brightly colored petals → Advertise plant, act as landing stage, guide bug’s movements to anther or stigma.
• Secreted scent from petals → Advertise plant
• Large, spiky pollen grains → Stick to insect, protein-rich food
• Large, sticky stigma → Collect pollen from visiting insects
• Glands (nectaries) secrete sugar solution (nectar) → Attractive to insects as energy source
• Nectaries positioned deep in flower → Insects must brush past anthers and stigma to reach the nectaries

Question 24

Define Seed Dispersal.

Answer 24

Movement of seeds (which can’t move themselves), often long distances away from parent plant. This:
* Reduces competition between offspring and parent.
* Helps spread the species.

Question 25

What structural aspects of the fruit affect seed dispersal?

Answer 25

* Dry and explosive * Fleshy and attractive for animals to eat * Feathery or winged to catch the wind * Covered in hooks that catch onto coats of animals

Question 26

What is self-incompatibility?

Answer 26

The converse of the immune system, where there is rejection of non-self proteins or cells. ## Footnote * Bad for fruit farmers, as planting a single variety may result in little to no fruit.

Question 27

How does self-incompatability occur?

Answer 27

* Has evolved more than once, different mechanisms exist. * However, all plants have a genetic basis with alternative alleles of one or more genes. * Plants with the same self-incompatibility alleles cannot successfully pollinate each other.

Question 28

Define Cross-Pollination.

Answer 28

Transfer of pollen from an anther in a flower on one plant to a stigma of a flower on another plant.

Question 29

What are some advantageous of cross-pollination?

Answer 29

* Leads to fusion of male and female gametes from different plants → Promotes genetic variation → Therefore, promotes evolution. * Essential at times of environmental changes. * Promotes “hybrid vigour”—the offspring of crosses between genetically unrelated plants tend to be healthy and grow strongly → May be due to having different alleles of many genes rather than to being homozygous.

Question 30

Define Hermaphrodite.

Answer 30

Plants that produce both pollen containing male gametes and ovules containing female gametes (makes self-pollination possible).

Question 31

Define Self-Pollination.

Answer 31

Transfer of pollen from an anther to a stigma on the same plant; Extreme example of inbreeding.

Question 32

What are shared features of insect-pollinated flowers?

Answer 32

* Large, brightly colored petals → Advertise plant, act as landing stage, guide bug’s movements to anther or stigma. * Secreted scent from petals → Advertise plant * Large, spiky pollen grains → Stick to insect, protein-rich food * Large, sticky stigma → Collect pollen from visiting insects * Glands (nectaries) secrete sugar solution (nectar) → Attractive to insects as energy source * Nectaries positioned deep in flower → Insects must brush past anthers and stigma to reach the nectaries

Question 33

How does sexual reproduction occur in plants?

Answer 33

Zygote produced in fertilization retained by female parent, and supplied with food as it grows and develops into an embryo. Embryo inside a seed, which is dispersed when female parent fully formed.

Question 34

What are the male parts of plants?

Answer 34

* Anther: Supported by stalk (‘the filament’). * Diploid cells inside anther divide by meiosis to produce four haploid cells. * Each develops into a pollen grain. * Nucleus inside pollen grain divides by mitosis, to produce three haploid nuclei—two of which are male gametes. Genes in third nucleus expressed during pollen development and fertilization. * Pollen grains develop thickened wall (with distinct patterns on exterior).

Question 35

What are the female parts of the plants?

Answer 35

* Have ovary and stigma, where pollen is received. * Connecting stigma to ovary is style (variable in length, hollow centre). * Ovary contains one or more ovules (ovoid in shape and multicellular). * One cell in centre of ovule grows particularly large, then divides by meiosis to produce four haploid nuclei. * One of these divides three times by mitosis to produce eight haploid nuclei—one of which is the female gamete or ‘egg’. * Others assist in fertilization and subsequent embryo development.

Question 36

How does successful sexual reproduction in plants occur?

Answer 36

* Successful sexual reproduction in flowering plants involves pollination, fertilization, and embryo development. * Pollination: Transfer of pollen from the anther to the stigma, usually by wind or animals. * Fertilization: Occurs inside the ovule in the ovary. Pollen tube grows down the style to the ovary, carrying male gametes to the female gamete (egg) in the ovule. Fertilization occurs when the male gametes meet the egg. * The result of fertilization is a zygote, which develops into an embryo with an embryo root, shoot, and one or two cotyledons (embryo leaves)

Question 37

What is flower reproduction considered sexual?

Answer 37

* Flower reproduction is sexual because it involves meiosis, gamete production, and fertilization. * Many flowers are hermaphrodite, containing both male and female parts, allowing them to act as both male and female parents. * Some flowers have only male or female parts, rather than both. * Male and female flowers can be on the same plant or on separate plants. * Sexual reproduction occurs as male gametes fertilize female gametes