S ection 6: S ex Cells and Fertilisation
U se the w ords in the w ord bank below to com plete the sentences below :
S maller, vagina, anther, halved, fertilisation, nucleus, male, half, gametes, D N A , stigma, female, ovules, pollen, pollen tube, four, zygote, threadlike, one, identical, genes, amino acids, protein, function, meiosis, sex chromosomes, male
S ome plants reproduce sexually. T he sexual parts are inside the flow ers. M ost flow ering plants have flow ers w ith both ______and ______parts. T hese sexual parts produce special sex cells called ______.
Label the diagram above.
T he male part of a flow ering plant is called the ______and produces ______. T he female part is called the ______and produces ovules.
Pollen grains are ______and more numerous than ovules, w hich are larger.
Fertilisation in flow ering plants occurs by pollen trains being transferred to the ______. A ______then grow s dow n into the ovary and into an ovule. A male gamete then passes dow n the tube and fuses w ith egg cell. T his process is called
1 ______. T he fertilised egg is now called a ______.
Fertilisation produces variety in the offspring because genetically identical gametes form in different w ays, producing different combinations.
S exual Reproduction In H umans Label the follow ing diagrams:
2 In humans, fertilisation takes place in the oviduct. S perm, w hich are placed in the ______sw im through the uterus and along an oviduct w here only __ ___ sperm fuses w ith the egg. T his results in the formation of a zygote. A zygote has __ ___ the genetic information from both parents.
T his type of fertilisation produces a greater variety of offspring. T his is because no tw o sperm or egg cells are ______. T his means that brothers and sisters cannot receive the same combination of parental characteristics.
A chromosome is ______structure that carries genetic information. T his information is stored in the ______of a cell. T he sections of a chromosome w hich contains separate pieces of information are called ______. H umans have 46 chromosomes in their chromosome compliment.
Chromosomes are made of a complex substance called ______. S trands of D N A have a chain like structure to w hich bases are attached. T here are __ __ different bases in D N A .
T he bases in D N A carry the code to make up ______. T hese molecules join up to make a larger ______molecule. T he proteins formed are then tw isted and folded in space to make different shapes. T he overall shape produced is important in determining the protein’s ______, e.g. the active site of an enzyme is specific to its substrate.
Label the diagram below :
A single chromosome A double chromosome
3 A gamete mother cell is a cell w hich produces gametes. T his is done by a type of division called ______. D uring this division, the total number of chromosomes is ______. V ariation is increased during gamete formation by the independent separation of pairs of chromosomes. T his occurs randomly so the gamete mother cell can produce many different combinations in the gametes.
O f the 23 pairs of chromosomes that humans have, one pair determines the sex of the individual and are called ______. Females have 2 X chromosomes, w hereas males have an X and a Y chromosome.
S ince females can only pass on an X chromosome, it is the ______that determines the sex of the offspring because sperm can be either X or Y
Label the offspring as male or female in the diagram below :
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