Sexual Reproduction

Topic 11.4

Essential idea: Immunity is based on recognition of self and destruction of foreign material.


11.4.U1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation

Diagram of spermatogenesis and oogenesis

11.4.U2 Processes and spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

Gamete numbers and amount of cytoplasm diagram

11.4.U3 Fertilization and animals can be internal or external

Comparison of internal and external fertilization

11.4.U4 Fertilization involves mechanisms that prevent polyspermy

The process of fertilization

Acrosomal and Cortical Reactions

The process of fertilization includes acrosomal reaction, penetration of the egg membrane by the sperm, the cortical reaction and diffusion of the sperm nucleus with the egg nucleus. After ejaculation the sperm moves through the uterus and enters the fallopian tube as it swims towards the egg attracted by chemicals (chemotaxis). Once sperm reach the egg it must swim through the follicle cells that surround the egg and move through the zona pellucida. The necessary reactions are shown in the figure below.

Placing your mouse pointer on the figure below will show the explanations for the acrosomal and cortical reactions.

The acrosomal and cortical reactions

Fertilization produces a diploid zygote

Fertilization produces a diploid zygote

11.4.U5 Implantation of the blastocyst in the endometrium is essential for continuation of pregnancy

Implantation of the blastocyst

After fertilization the diploid zygote moves down the fallopian tube and undergoes several mitotic divisions resulting in a hollow ball of cells called the blastocyst (shown below). The blastocyst implants in the uterine wall and begins to secrete a hormone called human chorionic gonadotropin space (HCG). The HCG maintains the production of estrogen and progesterone by the corpus luteum of the ovary during the first few months of pregnancy. If these hormones are not present, menstruation will occur, and the embryo will be spontaneously aborted.

Implantation of the blastocyst

11.4.U6 hCG stimulates the ovary to secrete progesterone during early pregnancy

Transfer of electrons in the thylakoid membrane
Explanation of the role of hCG

11.4.U7 The placenta facilitates the exchange of materials between the mother and fetus

The role of the placenta?

The figure below shows the structures of the placenta. The functions of the placenta include the secretion of the hormones estrogen and progesterone which help maintain the pregnancy and are explained by placing your mouse pointer on the figure. Note that the fetus supported and protected by the amniotic sac in the amniotic fluid and materials are exchanged between the maternal and fetal blood in the placenta.

Place your mouse on the figure to see the role of the placenta during pregnancy.

Functions of the placenta

11.4.U8 Estrogen and progesterone are secreted by the placenta once it has formed

Estrogen and progesterone secretion by placenta

11.4.U9 Birth is mediated by positive feedback involving estrogen and oxytocin

Diagram of the process of birth


11.4.A1 The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other animals


11.4.S1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

Place your mouse pointer on the diagram to view labelled structures.

Diagram of seminiferous tubules

Place your mouse pointer on the diagram to view labelled structures.

Diagram of ovary

11.3.S2 Annotation of diagrams of mature sperm and egg to indicate functions

Place your mouse pointer on the diagram to view labelled structures and functions of a sperm.

Diagram of sperm structures

Place your mouse pointer on the diagram to view labelled structures and functions of an egg.

Diagram of sperm structures
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