Animal Reproduction

Important definitions • Acrosome reaction – acrosome enzymes digest the corona radiata and the zona pellucida, allowing the sperm and oocyte membranes to fuse • Capacitation – changes in the sperm cell membrane that increases its fluidity and allows the acrosome reaction to occur • Cortical reaction – fusion of cortical granule and oocyte membranes, releasing their contents, which converts the zona pellucida to a fertilisation membrane • Implantation – the sinking of the blastocyst into the endometrium • Pregnancy – the time from the first day of the last period until birth • Tonoplast – cells forming the outer layer of the blastocyst

Reproductive systems Male > Female >

Spermatogenesis Production of spermatozoa in the seminiferous tubules • Diploid spermatogonia divide many times by mitosis to produce primary spermatocytes • Primary spermatocytes divide by meiosis I to form haploid secondary spermatocytes • Secondary spermatocytes complete meiosis II to form spermatids • Spermatids differentiate into haploid and mature spermatozoa

Oogenesis Production of ova in ovaries • Oogonia (formed before birth) divide my mitosis to produce primary oocytes • Primary oocytes divide by meiosis but are halted at prophase I • Germinal epithelium divide to form follicle cells which surround the oocytes to form primary follicles these divide further when stimulated by puberty initiated hormones • One follicle will mature into a fully developed graafian follicle • Primary oocyte completes meiosis I to form a secondary oocyte and a polar body • Mature graafian follicle migrates to the surface of the ovary where it bursts and releases the secondary oocyte (ovulation) • Empty graafian follicle becomes the corpus luteum (produces hormones during pregnancy but regresses if fertilisation does not occur) • Secondary oocyte begins meiosis II but stops at metaphase if fertilisation does not occur

Fertilisation Occurs in fallopian tubes • Sperm reach the ovum • (Capacitation) Chemicals are released from the cells surrounding the ovum, triggering the acrosome reaction • Acrosome swells and fuses with the sperm membrane • Digestive enzymes in the acrosome are released which digest through the follicle cell and the zona pellucida • Sperm fuses with the ovum membrane and the sperm nucleus enters the ovum • Cortical reaction occurs in the ovum and thickens the zona pellucida, ion channels in the ovum membrane open and close so the cell becomes positive (usually negative), preventing more sperm entering • Meiosis II in the female is now completed, resulting in a large ovum and a 2nd polar body • Nuclei of sperm and ovum fuse to form a zygote which will develop into an embryo

1 2 3 1 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Concentration of hormones secreted by pituitary gland Concentration of hormones secreted by ovary Thickness of uterus lining Changes in the ovary Menstruation Ovum development FSH LH Oestrogen Progesterone

1 2 3 1 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Concentration of hormones secreted by pituitary gland Concentration of hormones secreted by ovary Thickness of uterus lining Changes in the ovary Menstruation Ovum development FSH LH Oestrogen Progesterone 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Menstruation cycle 1. FHS stimulates development of primary follicles 2. FHS stimulates theca cells of the graafian follicles to produce oestrogen 3. Oestrogen stimulates the rebuilding of the uterus wall 4. Initial low levels of oestrogen inhibit FSH secretion (negative feedback) 5. Rising oestrogen stimulates release of LH 6. LH reaches maximum around day 12 7. Peak of LH causes ovulation around day 14 8. Oestrogen falls as follicle becomes corpus luteum

Menstruation cycle (Continued) 9. Corpus luteum produces progesterone, maintain the uterus lining 10. Progesterone rises and inhibits FSH and LH 11. Fall in FSH and LH due to oestrogen and progesterone (negative feedback) 12. If no fertilisation occurs, corpus luteum degenerates 13. Progesterone and oestrogen concentrations fall 14. Uterus wall begins to breakdown 15. FSH no longer inhibited so rises and stimulates release of a new follicle 16. If fertilisation does occur, the blastocyst produces HCG which maintains corpus luteum, producing oestrogen and progesterone

Hormones during pregnancy • Blastocyst secretes HCG around 6 days after fertilisation • Chorion (becomes outer layer of placenta) secretes HCG after implantation • HCG maintains corpus luteum which will continue to secrete progesterone for about 16 weeks of pregnancy • Progesterone maintains the endometrium and contributes to placenta structure • Oestrogen and progesterone inhibit FSH (no new follicles can mature), LH (ovulation is not possible) and Prolactin (no milk made) • Progesterone also inhibits oxytocin so myometrium and milk duct do not contract • Oestrogen stimulates the growth of the placenta, the growth of mammary glands and increases blood supply (during the menstrual cycle this stimulates release of LH, inhibits FSH and repairs the endometrium)

Hormones during and after birth • Just before birth, oestrogen levels rise and progesterone levels fall enabling the myometrium to contract • Oxytocin is secreted by pituitary gland which stimulates uterus wall to contract ant stimulate secretion of more oxytocin (positive feedback causing contractions) • Prolactin secreted from pituitary gland during and after birth to stimulate milk production

The Placenta and amniotic fluid Placenta functions > • Allows exchange of gases and nutrients between mother and foetus • Barrier between maternal and foetal blood (counter current) • Protection from maternal immune system • Protection from maternal higher blood pressure • Secretes hormones (oestrogen, progesterone and HCG) Amniotic fluid > • Acts as a shock absorber and protects foetus during development • Maintains foetal temperature • Provides lubrication • Allows movement so muscles and bones develop functioning before birth • Made up of 98% water foetal cells and a solution of urea, salts, a little protein and a trace of sugar

Plant Reproduction

Important definitions • Dehiscence – opening of the anther, releasing pollen grains • Dichogamy – stamen and stigma ripening at different times • Dormant – a seed when its active growth is suspended, germination will occur if conditions are met • Germination – biochemical and physiological process through which a seed becomes a photosynthesising plant • Pollination – transfer of pollen grains from the anther to the stigma of a plant of the same species • Protandry – stamen ripens before the stigma • Protogyny – stigma ripens before the stamen

Flower structure

Pollination Self-pollination > • Self-fertilisation • Dependent on random assortment and crossing over in meiosis and mutation to bring about genetic variation • Less genetic variation displayed by species using this technique • Inbreeding leads to less evolutionary significance Cross-pollination > • Cross-fertilisation • Variation brought about by meiosis and random fusion of gametes • More genetic variation displayed by species using this technique • Outbreeding so evolutionary significance

Pollination (Continued) Insect pollinated flowers > • Colourful petals, scent and nectar • Anthers inside the flower • Stigma inside flower • Small quantities of sticky pollen Wind pollinated flowers > • Small, green and inconspicuous with no scent and no petals • Anthers hang outside • Stigmas are large and feathery • Large quantities of small, smooth and light pollen

Gametogenesis Pollen grain formation > • Occurs in the anthers • Each anther contains 4 pollen sacs which contain diploid microspore mother cells • Microspores divide by meiosis to produce haploid microspores • Each nucleus divides by mitosis producing 2 haploid nuclei, a tube nucleus and a generative nucleus Egg cell formation > • Occurs in the ovule • Diploid megaspore mother cells divide by meiosis to produce 4 haploid megaspores • 3 megaspores disintegrate • The one left divides 3 times by mitosis resulting in an embryo sac containing an egg cell, 2 polar bodies and various small bodies

Pollination and fertilisation • Molecules on the surface of the pollen grain interacts with the stigma • If from the same species, the pollen grain begins to germinate/grow • A pollen tube grows out of the side of the pollen grain, through the stigma and hollow style, towards the ovary • The generative cell containing the generative nucleus travels down the tube and as it moves down, divides my mitosis and produces 2 male nuclei • Tip of the pollen tube passes through the micropyle of the ovule, male nuclei can pass into the ovule • One male nucleus fuses with the nuclei of 2 polar bodies forming a triploid nucleus (called the endosperm nucleus) and the other fuses with the egg cell to form a diploid zygote

Seed development • Ovule (embryo, endosperm and Testa) becomes the seed • Funicle of ovule becomes the funicle of the seed • Ovary becomes the fruit • Ovary wall may become sweet and juicy (cherries) or hard and dry (almonds) • Triploid endosperm nucleus becomes a food store for the developing embryo • Diploid zygote divides by mitosis to produce a plumule (embryonic shoot) and a radicle (embryonic root) plus one or two cotyledons (seed leaves) • Outer integument dries out and lignin is deposited inside making it a waterproof seed coat

Germination • Requires a suitable temperature, water and oxygen • Water is taken up by the seed through the micropyle which causes tissues to swell and gives enzymes mobility • Insoluble food reserves are broken down into soluble ones that dissolve in water, these are then transported to the plumule and radicle • Amylase hydrolyses starch into maltose, protease converts proteins to amino acids and some sugars are converted into cellulose for cell wall synthesis • Energy is released from sugars and amino acids are synthesised to make new proteins during anaerobic respiration • Radicle pushes its way through the seed coat first, radicle grows downwards and plumule grows upwards • During germination, cotyledons remain under ground • Once plumule emerges, the plant can photosynthesise (cotyledons would have been depleted by this point)

Change in dry mass of embryo/seedling and endosperm • Hydrolysis of food reserves in the endosperm and starch is converted to maltose • Dry mas of endosperm decreases because CO2 is lost when sugars are used in anaerobic respiration and sugars are sent to the embryo • Mass of embryo decreases as it receives sugars from the endosperm • Total mass will decrease at first as CO2 is lost during anaerobic respiration but increases as first leaves are produced and the plant can photosynthesise, producing biomass Total mass Endosperm Embryo / seedling