Gametes & Fertilisation

In humans, fertilisation typically occurs in the oviduct (fallopian tube). Sperm must travel from the vagina, through the cervix and uterus, to meet the egg shortly after ovulation has occurred.

In flowering plants, the process begins with pollination, where pollen lands on the stigma. A pollen tube then germinates and grows down through the style to reach the ovary, delivering the male nucleus directly to the ovule.

Once the nuclei fuse, the resulting zygote undergoes rapid cell division via mitosis. This process increases the cell count without changing the genetic makeup, eventually forming an embryo.

As the embryo grows, cells undergo differentiation, a process where they become specialized to form specific tissues and organs, such as muscle, nerve, or vascular tissue.

Terminology Precision: Always distinguish between 'pollination' and 'fertilisation' in plant biology. Pollination is merely the physical transfer of pollen to the stigma, while fertilisation is the actual chemical fusion of the nuclei.

Chromosome Math: If an exam question provides the diploid number ($2n$), always divide by $2$ to find the gamete count. For example, if a plant has $14$ chromosomes in its leaf cells, its pollen will have $7$.

Functional Reasoning: When asked about adaptations, link the structure to the function. For example, 'Sperm have many mitochondria to provide energy for swimming.' Simply stating they have mitochondria is often insufficient for full marks.

Sequence of Events: Remember the order: Meiosis $\rightarrow$ Gametes $\rightarrow$ Fertilisation $\rightarrow$ Zygote $\rightarrow$ Mitosis $\rightarrow$ Embryo.

Location Error: A common mistake is believing fertilisation in humans occurs in the uterus. In reality, it occurs in the oviduct; the uterus is the site of implantation and development, not the initial fusion.

Genetic Identity: Students often forget that while a zygote is a single cell, it is already genetically distinct from both parents. It is not a 'blend' but a unique combination of DNA.

Plant Motility: Do not assume plant pollen 'swims' like sperm. The pollen tube is a growth process, not a locomotion process.