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S ection 6: S ex Cells and

U se the w ords in the w ord bank below to com plete the sentences below :

S maller, , anther, halved, fertilisation, nucleus, male, half, , D N A , , , , , , four, , threadlike, one, identical, genes, amino acids, protein, function, , , male

S ome 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 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 and into an . A male then passes dow n the tube and fuses w ith . 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 In H umans Label the follow ing diagrams:

2 In , fertilisation takes place in the . S perm, w hich are placed in the ______sw im through the and along an oviduct w here only __ ___ 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 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 is specific to its substrate.

Label the diagram below :

A single chromosome A double chromosome

3 A gamete 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 ______. have 2 X chromosomes, w hereas males have an X and a .

S ince females can only pass on an , 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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