A biology teacher places Fig. 1 in a revision booklet. The diagram shows a sperm cell approaching an ovum. The cap at the front of the sperm contains enzyme...
Question 1 Report
A biology teacher places Fig. 1 in a revision booklet. The diagram shows a sperm cell approaching an ovum. The cap at the front of the sperm contains enzymes.
(a) Name the cap at the front of the sperm cell. [1]
(b) Explain how enzymes in this cap help fertilisation. [2]
(c) Describe what happens to the nuclei of the sperm and ovum during fertilisation. [2]
(d) Explain why a fertilised ovum usually has the normal human chromosome number. [3]
(e) State two changes that happen to the fertilised ovum before it implants in the uterus lining. [2]
(f) Which type of cell division makes sperm cells with half the usual chromosome number? [2]
Answer Details
(a) The cap at the front of a sperm cell is the acrosome. [1]
(b) Enzymes in the acrosome digest or break down the outer layers of the ovum. This allows the sperm to enter the ovum. [2]
(c) The sperm nucleus enters the ovum, then the sperm and ovum nuclei fuse. [2]
(d) A sperm cell has 23 chromosomes and is haploid. An ovum also has 23 chromosomes and is haploid. When their nuclei fuse, the zygote has 46 chromosomes and is diploid, the normal human chromosome number. [3]
(e) Before implantation, the fertilised ovum divides by mitosis and forms a ball of cells or early embryo. It also moves down the oviduct. Any two of these changes gain credit. [2]
(f) The cell division is meiosis. It produces haploid sperm cells with 23 chromosomes, half the usual chromosome number. [2]
Download The App On Google Playstore
Everything you need to excel in your exams
