D3.1 Reproduction

How does sexual or asexual reproduction exemplify themes of change or continuity? What changes within organisms are required for reproduction?

asexual reproduction

reproduction not involving gametes and fertilization, all offspring are genetically identical

sexual reproduction

reproduction involving the production and fusion of gametes involving two stages:

1. meiosis-special division that makes gametes with half the number of chromosomes

2. fertilization- fusion of female and male gametes to form a zygote

gamete

• haploid male or female sex cell that is able to unite with another of the other sex to form a zygote

• have unique sequence of alleles due to random assortment and crossing over

fertilization

random fusion of haploid male and female gametes to form a zygote with diploid number of chromosomes

meiosis

• nuclear division with daughter cells (gametes) containing half the number of chromosomes of the parent cell

• halves the normal chromosome number forming haploid cells

cytokinesis

splitting of cytoplasm in parent cell between daughter cells, following the division of the nucleus

diploid

cells with nuclei containing two sets of chromosomes

haploid

cells with nuclei containing one set of chromosomes

differences between sperm and egg

• sperm travels to egg so it is smaller and has fewer energy reserves

• many sperms must be produced so they are small

male reproductive system

• two testes situates in scrotum hanging outside the main body cavity (form optimum temp)- producing sperm and testosterone

• epididymis stores sperm and sperm ducts carry them in seminal fluid outside the body

• seminal vesicles and prostate gland

• penis containing spongy erectile tissue that can fill with blood for erection

testis

site of spermatozoa- sperm production and production of hormone testosterone

sperm

motile male gamete

sperm duct

tube carrying sperm from the epididymis to the urethra

seminal fluid (semen)

male reproductive fluid, containing spermatozoa in a liquid that supports the sperm

prostate gland

releases alkaline secretion that neutralizes and urine left in the urethra and aids sperm mobility

urethra

tube that runs from bladder to outside of the body, in males also conveys semen

penis

external male organ used for urination and sexual intercourse

female reproductive system

• ovaries near the base of abdominal cavity secrete hormones oestradiol and progesterone

• pair of oviducts that extend from uterus and open as funnels close to ovaries- they transport egg cells and are a site of fertilization

• uterus- size and shape of inverted pear has thick muscular wall and inner lining- endometrium which builds up every month for embryo

• vagina- muscular tube that can enlarge to allow entry of penis and exit of baby. it is connected to uterus at cervix and opens to the exterior at the vulva

oestradiol

oestrogen

ovary

female reproductive organ in which the female gametes are formed; gland which secretes oestradiol and progesterone

oviduct

tube connecting ovary to uterus; site of fertilization

uterus

the organ in which the embryo develops in female mammals

endometrium

the lining of the uterus

menstruation

shedding of the endometrium from the uterus

vagina

muscular canal leading from uterus to outside of the body

cervix

ring of muscles at neck of uterus

hormones in female reproductive system

• cyclical secretion of oestradiol and progesterone

• menstrual cycle in which concentrations of FSH and LH and oestradiol and progesterone change

• menstrual cycle consists of two cycles- ovarian and uterine

follicle-stimulating hormone FSH

hormone secreted by pituitary gland that stimulates the development of egg cell into mature ovarian folicle in the ovary

luteinizing hormone (LH)

hormone produced by pituitary gland that stimulates ovulation and corpus luteum formation

menstrual cycle

monthly cycle of ovulation and menstruation in females

ovarian cycle

monthly changes that occur to ovarian folicles leading to ovulation and formation of corpus luteum.

uterine cycle

cycle of changes to the uterus lining (approx 28 days)

hypothalamus

part of the forebrain that controls the release of FSH and LH by the anterior pituitary gland

hormone regulation in menstual cycle

1. secretion of FSH

2. growth of follicle and secretion of oestradiol

3. release of LH leading to ovulation

4. corpus luteum secretes progesterone

5. falling levels of LH and FSH allow corpus luteum to degenerate

osetradiol inhibits FSH

progesterone inhibits LH

changing levels of hormones in menstrual cycle

1. FSH secretion that stimulates development of ovarian follicle

2. developing follicle secretes oestradiol

3. oestradiol reaches peak mid cycle and inhibits further secretion of FSH, this prevents probablility that other follicles will develop (negative feedback)

4. high levels of oestradiol stimulate secretion of LH, which stimulates ovulation on day 14, ovarian follicle releases egg, LH stimulates conversion of the vacant follicle into corpus luteum

5. corpus luteum secretes progesterone and a little oestradiol

6. levels of FSH and LH decrease and allow corpus luteum to degenerate- levels of progesterone and oestradiol also fall- endometrium brakes down and is lost through vagina- falling levels of progesterone cause secretion of FSH

7. new cycle beigins

8. if the egg is fertilized then the developming embryo becomes endocrine gland and secretes a hormone thet maintains corpus luteum as an eendocrine gland- corpus luteum brakes down placenta takes over as endocrine gland and secretes osetradiol and progesterone

oestradiol

• ovarian folicle secretes it

• in uterus it stimulates build-up of endometrium for embryo

• leads to increase in FSH receptors increasing oestradiol production (positive feedback)

• reaches peak mid cycle and inhibits further secretion of FSH, this prevents probablility that other follicles will develop (negative feedback)

ovulation

release of oocyte from ovary

ovarian follicle

fluid-filled spherical sac that contains and nourishes and immature egg or oocyte

progesterone

• secreted by corpus luteum

• in uterus it continues build up of endometrium

• in pituitary gland it inhibits secretion of LH (negative feedback)

corpus luteum

a hormone-secreting structure that develops from an ovarian follicle after an oocyte has beed discharged. It degenerates after few days unless pregnancy has begun.

causes of infertility

• failure to achieve or maintain erect penis

• sperm with poor mobility

• too few sperm

• conditions of the cervix that cause death of sperm

• eggs that fail to mature or be released

• blocked or damaged oviducts, preventing egg from reaching sperm

In vitro fertilization IVF

medical procedure in which an egg is fertilized by sperm in a test tube

steps in IVF

1. shutting down the menstrual cycle by stoping secretion of hormones by nasal spray

2. superovulation- high doses of FSH are injected to stimulate development of multiple follicles

3. hCG is injected to start maturation process and follicles are collected

4. prepared eggs are combined with sperm

5. incubation

6. woman takes progesterone to maintain endometrium and aid implantation

7. embryos are placed in uterus

ovule

in the flowering plant flower, the structure in an ovary which after fertilization grows into the seed

pollen

male reproductive cells, microspore produced in anthers and male cones containing male gametes

pollination

transfer of pollen from anther to stigma

pollen tube

grows out of a pollen grain attached to a stigma and down through the style tissue to the embryo sac

hermaphrodite

carrying both male and female parts such as flowers

double fertilization

pollen tube delivers two male nuclei. One fuses with egg nucleus in embryo and other with another nucleus forming food store

difference between pollination and fertilization in flowering plant

sepal

green structures that cover the flower while it is developing

petal

large, colourfull structure that attracts pollinators to the flower

stamen

male part of the flower consisting of the anther and filament

anther

produces pollen, which contains male gamete

filament

structure that holds up the anther, presenting it to visiting animals

carpel

female part of the flower made from the stigma, style and ovary

stigma

the part of the female reproductive organs where pollen lands

style

holds up stigma and is the path down which the pollen tube grows, carrying nuclei to the ovum.

cross-pollination

pollen transferred from the anther of one flower to the stigma of another flower of the same species by animals; it is achieved by: stamen and stigma maturing at different times, stigma and anthers at different heights, separate male and female flowers

self-pollination

when pollen is transferred to the stigma in the same flower; advantage: preserves good genomes; disadvantage reduction in variation

hermaphodite

structures carrying both female and male parts

seed

develops from the fertilized ovule and contains an embryo plant and food store

germination of seed

1. zygote grows by mitotic division to produce cells from an embryonic plant

2. formation of stored food reserves, food store is absorbed into cotyledons- occurs only if fertilization happens

3. seed matures, outer layers of ovule become protective coat or testa, ovary develops into fruit \

4. water content decreased and seed moves into dormancy period.

embryonic plat

consists of an embryo root, embryo stem and either a single cotyledon (seed leaf) or two cotyledons

seed dispersal

the carrying of the seed away from the parent plant, it is needed to reduce competition for space, light, nutrients and water

difference between seed dispersal and pollination

pollination transfers pollen from one plant to another, seed dispersal is when plant’s seeds are moved to new areas for germination

methods of seed dispersal

• wind

• water

• mechanical

• animal

germination

the resumption of growth by embryonic plant in seed or fruit, at the expense of stored food

dormancy of seed (spoczynek)

• incomplete seed development- causes embryo to be immature

• presence of plant growth regulator- abscisic acid that inhibits development

• impervious seed coat- eventually made permeable ex. abrasion with coarse soil

• requirement for pre-chilling- seed needs moist conditions to germinate

conditions needed for seed to germinate

• water uptake- seed hydrated and embryo physiologically active

• oxygen presence- aerobic respiration is sustained therefore there is enough energy for growth

• suitable temperature- mobilization of stored food reserves and enzyme action

gibberellic acid GA

plant growth substance produced by cells of the embryo, passes to the food stores in cotyledons, where protein is converted to hydrolytic enzymes that mobilize stored food reserves. Production of amylase which hydrolyses starch to maltose then to glucose

metabolic events of germination

1. water absorption that causes testa to split

2. embryo produces GA

3. GA passes to food storage cells

4. production of hydrolytic enzymes, conversion of starch to glucose and proteins into amino acids

5. glucose and amino acids are translocated to growing points of stem and root

6. growth and development occur in stem and root

7. seedling emerges and eventually becomes a self-sufficient autotrophic plant

puberty

the stage in life triggered by hypothalamus when an individual becomes sexually mature (secondary sexually characteristics develop), marking the transition from childhood to adulthood

similarity between testosterone, oestradiol and progesterone

• they are manufactured from steroid cholesterol that is both made in liver and absorbed as part of diet,

• they are anabolic steroids- they build up

secondary sexual characteristics in women

maturation of ovaries, enlargement of vagina and uterus, development of breasts, widening of pelvis, menstruation,

secondary sexual characteristics in male

development and enlargement of testes, scrotum, penis, increased skeletal muscle development, enlargement of larynx, deepening of voice, continous production of sperm

gonadotropin-releasing hormone GnRH

hormone that causes the pituitary gland to secrete luteinizing hormone LH and follicle stimulating hormone FSH, which enhance secretion of sex hormones and development of secondary sexual characteristics and prep for reproduction

gametogenesis

production of sex cells (gametes) by mitosis to proliferate cells that will undergo meiosis in testes and ovaries

meiosis I

• prophase- chromosomes condense and pair up becoming bivalents, centrioles duplicate, chromosomes now have chromatids

• metaphase- nuclear membrane breaks down, spindle forms, bivalents line at equator attached by centromeres, bivalents start to separate

• anaphase- homologous chromosomes separate towards poles of the spindle,

• telophase- nuclear membrane reforms, chromosome number has been halved, spindle breaks down

products: secondary spermatocytes and secondary oocytes

meiosis II

• prophase- chromosomes condense, centrioles duplicate and move to poles

• metaphase- nuclear membrane breaks down and spindle reforms, chromosomes attach to spindle fibres by centromere at the equator

• anaphase- centromeres divide and chromatids are pulled to opposite poles of spindle

• telophase- chromatids decondense, nudlear membrane reforms, nucleoli reform, there are now 4 cells, each with half the chromosome number

products: spermatids and ova

phases of gametogensis

1. multiplication- mother gamete cells divide mitotically

2. growth- each developing sex cell grows

3. maturation- meiosis and formation of haploid gametes

spermatogenesis

production of sperm in the testes, begins at puberty and continues throughout life, testes consist of seminiferous tubules which are lined by germinal epithelial cells that divide repeatedly. Tubules drain into channels leading to epididymis and sperm duct.

seminiferous tubule

elongated tubes in the testes, the site of sperm production, between individual tubules is connective tissue containing blood capillaries together with intersitial cells which secrete hormones, germinal epithelial cells inside are attacged to basement membrane along with nutritive cells.

phases of spermatogenesis

1. germinal epithelium cell of seminiferous tubule (2n) (sperm mother cell)

2. multiplication by repeated mitotic cell division

3. meiosis I where it divides into secondary spermatocytes (n)

4. meiosis II where secondary spermatocytes divide into spermatids which grow into sperm

spermatogonia

male germ cells (stem cells) which make up the inner layer of the lining of seminiferous tubules and give rise to spermatocytes

spermatocyte

cell formed in seminiferous tubules of testes, develops into sperm

spermatid

cells derived from secondary spermatocytes in the second mitotic division, which then differentiate into mature sperm

sertoli cells

large cells in the eminiferous lining that nourish developing sperm and on which they are dependent until they mature into spermatozoa

seminiferous tubule structure

testis tissue in section

stages of sperm development

• spermatogonium- 2n cells made by mitosis from cells lining the seminiferous tubules

• primary spermatocyte- 2n cells produced by mitosis, undergoes meiosis to make secondary spermatocyte

• secondary spermatocyte- n cells made from meiotic division

• spermatid- n cells made from second meiotic division

• spermatozoon/sperm- n spermatids differentiate into mature spermatoza

production of semen vs spermatogenesis

semen is sperm and the fluid form the prostate and seminal vesicles that the sperm travel in, while spermatogenesis is the process of sperm formation

hormones in spermatogenesis

• FSH - initiate sperm production in testes

• LH stimulates endocrine cells of testes to secrete testosterone

• testosterone and FSH maintain sperm production and growth of sertoli cells that support sperm with nutrients

• testosterone is regulated by negative feedback control- too much test inhibits secretion of LH, only when LH concentration drops the testosterone will be produces

ovary in section

ovulation

process by which egg is released to oviduct and occurs at the secondary oocyte

oogenesis

development of ovum in ovaries,

germinal epithelium which lines the outer surface of the ovary divides by mitosis to form oogonia which migrate into connective tissue of ovary where they transform into oocytes. Each oocyte becomes surrounded by follicle cells and it is then called primary follicle.

by mid pregnancy production of oogonia in foetus ceases, and many degenerate. Fewer than 1% will complete development.

between puberty and menopause primary follicles develop and grow, at the same time follicles move to outer part of ovary. primary follicle undergoes meiosis I but it is unequal creating tiny polar body and secondary oocyte. Meiosis II then begins but is not complete. Egg cell is released from ovary by rupture of follicle wall.

oogonia

immature female sex cells in the process of developing into an oocyte

oocyte

female sex cell in the process of meiotic division to become an ovum

stages in oogenesis

1. germinal epithelium- oogonia formed by mitosis in ovaries during development of foetus in uterus,

2. oogonia grow to become oocytes

3. primary follicles- oocyte surrounded by a layer of follicle cells

4. each menstrual cycle a few primary follicles start to develop- meiosis I is completed, forming a secondary oocyte and the first polar body (unequal division of cytoplasm) which fails to develop further

5. secondary oocyte in mature ovarian follicle with layers of follicle cells and fluid early in prophase of meiosis II (further development is then suspended until arrival of sperm in oviduct)

6. follicle bursts at ovulation and egg cell (secondary oocyte) released (surrounded by follicle cells)

7. remains of follicle now develop into endocrine gland- corpus luteum

8. corpus luteum degenerates quickly if fertilization does not occur

differences between spermatogenesis and oogenesis

1. spermatogenesis works almost whole life since puberty whereas oogenesis stops at 55 at menopause

2. spermatogenesis creates millions of sperm cells every day vs oogenesis creates one egg a month

3. spermatogenesis creates 4, small, mobile sperm cells vs oogenesis creates 1 big egg

4. spermatogenesis is controlled by test and FSH and oogenesis by progesterone, oestradiol, LH and FSH