Section 6: Sex Cells and Fertilisation

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 : 4.

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