▶️ Answer/Explanation
(a) Other Characteristics:
Any two from: Movement, Respiration, Sensitivity, Growth, Excretion, or Nutrition. (Often remembered by the acronym MRS GREN).
(b) Stages of Reproduction:
(i) Egg cell (or Ovum/Oocyte). Cell X is the female gamete.
(ii) Fertilisation. This is the fusion of the sperm nucleus with the egg nucleus.
(iii) Zygote. This is the diploid cell formed immediately after fertilisation.
(iv) Stage $4$. The zygote divides to form a ball of cells (embryo) which travels to the uterus and implants into the lining.
(c) Pregnancy Structures:
(i) X – Placenta; Y – Umbilical cord.
(ii) Part Z is the amniotic fluid. Its main functions are to protect the fetus against mechanical shock (bumps/knocks), maintain a constant temperature, and prevent the fetus from drying out.
(a) Characteristics of Life:
All living organisms share seven distinct characteristics defined by the syllabus (Topic 1.1): Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.
(b) Human Reproduction:
Sexual reproduction involves the fusion of two haploid gametes (sperm and egg) to form a diploid zygote (Topic 16.4). The process shown in Fig 8.1 begins with the sperm approaching the egg cell (Stage $1$). Stage $2$ leads to fertilisation, where nuclei fuse. The resulting single cell (Stage $3$, the zygote) undergoes mitosis to form a ball of cells (Stage $4$, often called a blastocyst/morula), which implants in the uterus wall to develop into an embryo and then a fetus.
(c) Pregnancy:
During development (Topic 16.4), the fetus is supported by several structures:
X (Placenta): Anchors the fetus to the uterus and facilitates the exchange of nutrients, gases (oxygen/carbon dioxide), and waste between the mother’s blood and the fetus’s blood.
Y (Umbilical Cord): Contains blood vessels that connect the fetus to the placenta.
Z (Amniotic Fluid): Contained within the amniotic sac, this fluid cushions the fetus from external physical impact and allows for movement.