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The chemical constituents of cytoplasm (that part of the cell outside the nucleus) are not resynthesised from DNA every time a cell divides. This is because each of the two daughter cells formed during cell division usually inherits about half of the cellular material from the mother cell (see cell: Cell division and growth), and is important because the presence of essential enzymes enables DNA to replicate even before it has made the enzymes necessary to do so.

Cells of higher organisms contain complex structures, and each time a cell divides the structures must be duplicated. The method of duplication varies for each structure, and in some cases the mechanism is still uncertain. One striking and important phenomenon is the formation of a new membrane. Cell membranes, although they are very thin and appear to have a simple form and structure, contain many enzymes and are sites of great metabolic activity. This applies not only to the membrane that surrounds the cell but to all the membranes within the cell. New membranes, which seem to form rapidly, are indistinguishable from old ones.

Thus, the formation of a new cell involves the further synthesis of many constituents that were present in the parent cell. This means that all of the information and materials necessary for a cell to reproduce itself must be supplied by the cellular constituents and the DNA inherited from the parent cell.

Men and women have different reproductive organs. A woman's ovaries produce egg cells, and her uterus can carry a developing baby. A man's testes produce sperm. Other glands add fluids to the sperm.

Encyclopædia Britannica. (n.d.). reproductive system. [image]. Britannica School. Retrieved April 3, 2023, from https://school-eb-com-au.db.plcscotch.wa.edu.au/levels/high/assembly/view/154385

Hormones in human reproduction

Hormones are the drivers of human reproduction, responsible for sexual development and controlling the menstrual cycle.

Key hormones

Sex hormones are responsible for driving sexual development (puberty). The main reproductive hormones are oestrogen and testosterone.

Oestrogen causes eggs to mature in ovaries once a girl hits puberty. These are then released at regular intervals during the menstrual cycle. Testosterone stimulates sperm production in males.

Other hormones involved in the menstrual cycle include:

• Follicle stimulating hormone (FSH), causing maturation of an egg in the ovary.
• Luteinising hormone (LH) stimulating the release of the egg.
• Oestrogen and progesterone are involved in maintaining the uterus lining.

Society for Endrocrinology. (n.d.). You and your hormones. You and Your Hormones. https://www.yourhormones.info/students/topics/hormones-in-human-reproduction/

A life cycle is a series of stages a living thing goes through during its life. All plants and animals go through life cycles. In this video you’ll see the life cycle of a dandelion and a bird.

Reproduction in flowering plants begins with pollination, the transfer of pollen from anther to stigma on the same flower or to the stigma of another flower on the same plant (self-pollination) or from the anther on one plant to the stigma of another plant (cross-pollination). Once the pollen grain lodges on the stigma, a pollen tube grows from the pollen grain to an ovule. Two sperm nuclei then pass through the pollen tube. One of them unites with the egg nucleus and produces a zygote. The other sperm nucleus unites with two polar nuclei to produce an endosperm nucleus. The fertilised ovule develops into a seed.

Encyclopædia Britannica. (n.d.). how flowering plants reproduce . [image]. Britannica School. Retrieved April 3, 2023, from https://school-eb-com-au.db.plcscotch.wa.edu.au/levels/high/assembly/view/53831