IB BIO SL D3.1

Compare asexual and sexual reproduction in terms of genetic offspring outcomes and environmental advantages.

• Asexual: Produces genetically identical offspring (clones). Advantage: Rapid reproduction of individuals already adapted to a stable, existing environment.

• Sexual: Produces offspring with new gene combinations. Advantage: Generates genetic variation required for adaptation to changing environments.

How do meiosis and gamete fusion (fertilization) contribute to genetic variation in sexual life cycles?

• Meiosis: Breaks up existing parental allele combinations (via crossing over and independent assortment) to produce haploid gametes.

• Fertilization: Combines alleles from two distinct gametes to form brand-new allele combinations in the diploid zygote.

What is the primary difference between male and female gametes, and what reproductive strategy differences result from it?

• Prime Difference: The male gamete travels to the female gamete, making it smaller with fewer nutrient/food reserves than the egg.

• Strategies: Males produce vast quantities of small, mobile gametes (low investment per cell); females produce fewer, larger, non-motile eggs loaded with nutrient reserves (high investment per cell).

State the names and primary functions of the main structures in the human male and female reproductive systems

• Male: Testes (sperm/testosterone production), Epididymis (sperm maturation/storage), Vas deferens (sperm transport), Seminal vesicles & Prostate (secrete seminal fluid).

• Female: Ovaries (oocyte/estrogen/progesterone production), Oviduct/Fallopian tube (fertilization site/egg transport), Uterus/Endometrium (implantation/fetal development), Cervix & Vagina (sperm entry/birth canal).

Outline the roles and feedback mechanisms of FSH, oestradiol, LH, and progesterone during the menstrual cycle.

• FSH: Stimulates follicle growth and oestradiol secretion.

• Oestradiol: Thickens endometrium; high levels trigger a surge in LH via positive feedback.

• LH: Triggers ovulation and corpus luteum formation.

• Progesterone: Maintains endometrium; along with oestradiol, inhibits FSH and LH via negative feedback. Drop in progesterone causes menstruation

Describe the exact cellular and nuclear events that occur during human fertilization.

• Sperm and egg cell membranes fuse.

• Sperm nucleus enters the egg; sperm tail and mitochondria are destroyed.

• Nuclear membranes of both sperm and egg dissolve.

• Condensed chromosomes from both parents participate in a joint mitosis to form two diploid nuclei.

How are hormones manipulated during In Vitro Fertilization (IVF)?

• Down-regulation: Normal pituitary hormone secretion (FSH/LH) is suspended/paused using drugs.

• Superovulation: Artificial doses of FSH (and LH) are injected to induce simultaneous maturation of multiple follicles.

Where are gametes produced in flowering plants, and why is plant reproduction considered sexual even in hermaphroditic species?

• Gametes develop inside ovules (female) and pollen grains (male).

• It is sexual because it relies on the fusion of two haploid gametes (fertilization) to produce a genetically unique diploid embryo inside a seed, even if produced by a single plant.

Describe the key structural features and functions of an insect-pollinated flower.

• Petals: Large, colorful, scented to attract pollinators.

• Nectary: Secretes nectar as a food reward.

• Anthers: Produce sticky/spiky pollen; positioned inside where visiting insects brush against them.

• Stigma: Sticky surface positioned internally to collect pollen from insects.

State three adaptations/mechanisms plants use to promote cross-pollination.

• Temporal separation: Pollen and stigma mature at different times on the same plant.

• Structural/Gender separation: Separate male/female flowers on the same plant (monoecious) or separate male/female plants (dioecious).

• Vectors: Utilizing animal pollinators (bees, birds) or wind to transport pollen across distances.

State three adaptations/mechanisms plants use to promote cross-pollination.

• Temporal separation: Pollen and stigma mature at different times on the same plant.

• Structural/Gender separation: Separate male/female flowers on the same plant (monoecious) or separate male/female plants (dioecious).

• Vectors: Utilizing animal pollinators (bees, birds) or wind to transport pollen across distances.

What is the negative consequence of self-pollination, and how do self-incompatibility mechanisms prevent it?

• Consequence: Self-pollination leads to inbreeding, decreasing genetic diversity and population vigour.

• Mechanism: Genetic self-incompatibility systems allow the pistil to recognize self-pollen alleles and arrest pollen tube growth, ensuring only gametes from different plants fuse.

Distinguish seed dispersal from pollination, and outline the mobilization of food reserves during germination.

• Distinction: Pollination transfers pollen to the stigma; seed dispersal distributes mature seeds away from the parent to reduce competition.

• Germination Mobilization: Water absorption —> Gibberellin production —> Amylase synthesis —> Starch broken down into maltose/glucose —> Respiration powers embryo growth.