Reproduction and Growth
Reproduction of a Flowering Plant
Sepal: Protect the flower whilst its a bud
Petal: To attract insects and small animals for pollination, also protects the flower.
Stamen: Made up of the anther (produces pollen grains) and Filament (supports the anther and holds it in optimum position for pollen grains to be dispersed).
Carpel: Made up of the Stigma (where pollen grains land), Ovary (develops into fruit and contains ovule[s]) and Style (holds stigma).
Receptacle: Tissue from which all other parts originate
Formation of Male Gametes
- Each anther has four chambers = Pollen Sacs; lined with epidermis and fibrous layer.
- Pollen sacs have a layer of diploid cells = microspores (mothercells)
- Microspores divide by mitosis into 4 pollen cells called a tetrad
- The tetrad splits to form 4 individual pollen grains
- Each immature pollen has a single haploid nucleus which divides by mitosis into a tube nucleus and a generative nucleus.
- Generative nucleus undergoes a second round of mitosis to form 2 sperm nuclei
- Pollen grain forms a thick outer wall = Exine and a thin inner wall = Intine
- Pollen grains are formed inside the anther - when the pollen grains are mature the anther breaks open and the walls of the pollen sacs fold back so that the pollen is exposed.
Formation of Female Gametes
Ovule: Where seeds are formed
- Has two walls = Integuments
- Small opening = Micropyle, allows spern nucleus to enter the ovule
- Bulk of the ovule = Diploid nourishing cells; nucellus
Megaspore Mother Cell: Single diploid cell in the ovule
- Cell divides by meiosis = forms the embryo sac with 4 haploid nuclei
- 3 of the nuclei die. The forth goes through 3 rounds of mitosis to form 8 haploid nuclei.
- 2 of the nuclei form the polar nuclei and one becomes the egg nucleus
Pollination: Transfer of pollen from an anther to a carpel of the same species
Self-Pollination: Anther pollinates a carpel of the same plant; produces weaker offspring
Cross-Pollination: Anther pollinates a carpel on a different plant; produces stronger and healthier offspring
Methods of Cross Pollination
Animal
- Petals are large, scented and colourful to attract animals
- Smaller amounts of pollen which is sticky and large
- Anthers are smaller and inside the petals
- Stigmas are also smaller and inside the petal
- Example: Orchids
Wind
- Petals are small green and have no scent
- Pollen is in huge amounts, is small
- Anthers are large and are outside the petals
- Stigmas are large and feathery to catch pollen
- Examples: Grass, Oak
Animal
- Petals are large, scented and colourful to attract animals- Smaller amounts of pollen which is sticky and large
- Anthers are smaller and inside the petals
- Stigmas are also smaller and inside the petal
- Example: Orchids
Wind
- Petals are small green and have no scent
- Pollen is in huge amounts, is small
- Anthers are large and are outside the petals
- Stigmas are large and feathery to catch pollen
- Examples: Grass, Oak
Fertilisation
Fusion of male and female gametes to form a diploid zygote
1) Pollen grain lands on the stigma of the same species
2) Tube nucleus forms the pollen tube through the style
3) Generative nuclei enter the ovule through the micropyle and the tube nucleus dies
4) One of the nuclei fertilise the egg cell (2n) to form a diploid zygote
5) The other fertilises the polar nuclei (3n) to form the triploid endosperm
Seed Formation
After fertilisation the ovule becomes the new seed
- The integuments become the new seed coat
- The diploid zygote becomes the plant embryo and develops the plumule, radicle and cotyledon(s)
- The triploid endosperm divides by mitosis and absorbs the nucellus to store food
Types of Seeds
Endospermic: Plant embryo increases in size and only absorbs some of the endosperm
Non-Endospermic: Plant embryo increases in size and absorbs all of the endosperm in the process
Dicot Seeds
- Cotyledons absorbs food from the endosperm and store it
- Cotyledons pass food to the seed at germination
- Generally there is no endosperm at seed maturity
Monocot Seeds
- Tend to be endospermic
- One seed leaf
- Whilst germinating food is obtained from the endosperm and is passed to the seed
Testa: Outer layer of the seed, Strong to protect it.
Fruit Formation
To encourage the dispersal of seeds by animals
True Fruits: Fruits which develop from the ovary
False Fruit: Fruits which develop from the recepticle
Seedless Fruits
- Natural Genetic Manipulation
Seedless due to changes in their chromosome number
The egg cell/pollen grain are not viable and because of the no seed develops
- Artificial Genetic Manipulation
Similar to above except it is induced artificially
Number of chromosomes makes the embryo unviable and no seed develops
- Auxin Treatment
Sprays plant with auxins, stimulates the ovary to swell with food before fertilisation
- Ethene ripens fruit by making cell walls less rigid, it is also responsible for leaf fall during autumn
Fruit and Seed Dispersal
1) Wind Dispersal e.g. Dandeline
2) Water Dispersal e.g. Coconut trees
3) Animal Dispersal e.g. Berries
4) Self Dispersal e.g. pea pods
Dormancy
Resting period for the seed in which it undergoes no growth
Advantages
- Time for seed dispersal
- Time for embryo development
- Avoid harsh winter
- Germination at the start of the year; time to develop against following winter
- Staggered germination in the springtime creates less competition
* Growth regulator for dormany = Abscisic Acid
Reasons
- Decrease in temperature
- Growth promoter levels low within seed
- Abscisic acid levels high
Agriculture and Horticulture
Dormancy is useful for germinating seeds at the same time
Methods to break dormancy
- Scarification; Damaging seed coat to allow oxygen and water in
- Pre-chilling; Store seeds at a low temperature for a certain period of time
- Treatment with growth regulators
Germination
Regrowth of a plant embryo after a period of dormancy when environmental conditions are suitable. Caused by the reactivation of metabolism in the plant embryo.
Factors Necessary
1) Embryo must be alive
2) Factors preventing germination must be overcome e.g. if abscisic acid levels are still high within the seed it won't germinate.
3) Ideal environmental conditions needed;
- Oxygen; Required for seed respiration and subsequent metabolic reactions
- Water; Needed to wash away dormancy inhibitors, median for metabolic reactions, takes part in digestion.
- Suitable temperature; Needed to provide optimum temperature for enzymes
Role of Digestion
- Food reserves stored in the endosperm and/or the cotyledons
Lipids broken down to glycerol and fatty acids
Starch broken down to Glucose
Protein broken down to Amino Acids
- Food reserves needed until the plant can push itself through soil and photosynthesise
Respiration
To provide ATP needed for anabolic reactions
Dry Weight = Mass of seed - Water
Stages of Seedling Growth
Cotyledons move above the ground during germination and start to photosynthesise
- Seed absorbs water and swells
- Radicle (embryonic root) grows and absorbs water and minerals
Either
- Cotyledons pulled out of seed coat and moves above soil to photosynthesise, testa left behind in the soil.
or
- Entire seed pushed through the soil, Cotyledons remain enclosed in the testa until the reach the surface where the testa falls off and the cotyledons begin to photosynthesise.
- In both causes the plumule (embryonic shoot) is protected by the cotyledons, it is exposed when the cotyledons separate.
- The epicotyl which lies above the plumule begins to grow and leaves are formed
Investigate Factors Affecting Germination
- Place Tubes A, C and D in an incubator and Tube B in a fridge.
- Leave for 2-3 days.
Result: Only test tube A germinates as it contains all the necessary conditions for germination.
Investigate the Digestive Activity of a Germinating Seed
- Leave both plates in an incubator for a few days and afterwards pour iodine over the plates
Results:
- Area under the living seeds should stay red-yellow, thus showing that the seeds digest starch
- Area under the dead cells will change blue black showing the they didn't digest any starch
Reasons
- Decrease in temperature
- Growth promoter levels low within seed
- Abscisic acid levels high
Agriculture and Horticulture
Dormancy is useful for germinating seeds at the same time
Methods to break dormancy
- Scarification; Damaging seed coat to allow oxygen and water in
- Pre-chilling; Store seeds at a low temperature for a certain period of time
- Treatment with growth regulators
Germination
Regrowth of a plant embryo after a period of dormancy when environmental conditions are suitable. Caused by the reactivation of metabolism in the plant embryo.
Factors Necessary
1) Embryo must be alive
2) Factors preventing germination must be overcome e.g. if abscisic acid levels are still high within the seed it won't germinate.
3) Ideal environmental conditions needed;
- Oxygen; Required for seed respiration and subsequent metabolic reactions
- Water; Needed to wash away dormancy inhibitors, median for metabolic reactions, takes part in digestion.
- Suitable temperature; Needed to provide optimum temperature for enzymes
Role of Digestion
- Food reserves stored in the endosperm and/or the cotyledons
Lipids broken down to glycerol and fatty acids
Starch broken down to Glucose
Protein broken down to Amino Acids
- Food reserves needed until the plant can push itself through soil and photosynthesise
Respiration
To provide ATP needed for anabolic reactions
Dry Weight = Mass of seed - Water
Stages of Seedling Growth
- Epigeal
Cotyledons move above the ground during germination and start to photosynthesise
- Seed absorbs water and swells
- Radicle (embryonic root) grows and absorbs water and minerals
Either
- Cotyledons pulled out of seed coat and moves above soil to photosynthesise, testa left behind in the soil.
or
- Entire seed pushed through the soil, Cotyledons remain enclosed in the testa until the reach the surface where the testa falls off and the cotyledons begin to photosynthesise.
- In both causes the plumule (embryonic shoot) is protected by the cotyledons, it is exposed when the cotyledons separate.
- The epicotyl which lies above the plumule begins to grow and leaves are formed
- Hypogeal
Cotyledons remain below the soil
- Epicotyl grows rapidly and pushes the plumule above the soil
- Leaves are produced and photosynthesis occurs
Investigate Factors Affecting Germination
- Place Tubes A, C and D in an incubator and Tube B in a fridge.
- Leave for 2-3 days.
Result: Only test tube A germinates as it contains all the necessary conditions for germination.
Investigate the Digestive Activity of a Germinating Seed
Using Starch agar plates
- Leave both plates in an incubator for a few days and afterwards pour iodine over the plates
Results:
- Area under the living seeds should stay red-yellow, thus showing that the seeds digest starch
- Area under the dead cells will change blue black showing the they didn't digest any starch
Vegetative Propagation
Asexual reproduction in plants, production of a new individual from one parent plant. New organism is genetically identicle to the parent
- Faster than sexual reproduction
Natural Vegetative Propagation
1) Stem
e.g. Strawberries which send out runners/stolons
2) Root
e.g. Raspberries send out root sprouts/suckers
3) Leaf
e.g. Devils backbone
4) Bud
e.g. Onion bulb
Artificial Vegetative Propagation
1) Cutting - Removing small pieces of a parent plant and encouraging it to grow into a independent plant. May require rooting powder
2) Layering - Stem of the parent plant is bent down into the soil and encouraged to grow into a separate plant
3) Grafting - When the shoot system of one plant is joined with the root system of another
4) Tissue Culture/Micropropagation - Growth of a large number of plantlets in a nutrient medium from a small tissue sample.
Sexual Reproduction in the Human
Male Reproductive System
Prostate Gland, Seminal Vesicle, Cowpers Gland: All contribute to the production of semen, fluid in which sperm swim.
Sperm Duct: Carry sperm from the testes to the urethra.
Epididymis: Storage organ for sperm
Scrotum: Holds the testis outside the body, to keep the testis at a lower temperature as enzymes required in the production of sperm have a lower optimum temperature.
Testis: Produce sperm in response to follicle stimulating hormone, which is secreted by the pituitary. Testis are also responsible of the production of testosterone which is in response to lutinising hormone produced by the pituitary. Testosterone maintains male secondary sexual characteristics and plays a role in the production of sperm.
Penis: A muscular organ through which urine and semen travel.
Production of sperm: Produced by meiosis in the testis and is a highly specialised cell containing 3 parts.
- Head: Contains the nucleus with a haploid number of chromosomes and an acrosome to allow sperm to enter the egg cell.
- Midpiece: Contains many mitochondria to provide energy for the sperm to swim.
- Tail: Propels the sperm cell
- Midpiece: Contains many mitochondria to provide energy for the sperm to swim.
- Tail: Propels the sperm cell
Female Reproductive System
Fallopian Tube: Receives the egg from the ovaries and is the site of fertilisation.
Ovary: Secretes female sex hormones, produces the egg cell. Egg cells are present in the female body from birth and ovulation begins at puberty. Usually one egg released per 28 days.
Endometrium: Lining of the uterus, to prepare for pregnancy and is maintained throughout pregnancy.
Cervix: Junction between the vagina and the uterus
Vagina: Muscular tube which receives penis during intercourse and is also know as the birth canal. Cells lining the vagina secrete mucous to protect against infections.
Vulva: External female genitalia
Uterus: Where the fetus develops
Oestrogen: Produced in the ovaries in response to FSH. Responsible for maintaining female secondary sexual characteristics and repairs the endometrium during the menstrual cycle.
Progesterone: Produced in the ovaries following ovulation. Responsible for maintain endometrium during parts of the menstrual cycle and throughout pregnancy.
Meiosis: Is important in sexual reproduction to maintain the number of chromosomes in the offspring. It also enables variation through independent separation of chromosomes and swapping of the genes - crossing over.
Secondary Sexual Characteristics
Features which distinguish males from females but are not part of the reproductive system.
Males
- Facial hair
- Pubic hair
- Enlargement of larynx and deepening of voice.
- Broadening of shoulders and chest
Females
- Pubic hair
- Growth of breasts
- Enlargement of hips
The Menstrual Cycle
- Follicular Phase
Menstruation: Shedding of the uterus lining.
- Caused by the decreased levels of progesterone and oestrogen as a result of the degeneration of the corpus luteum.
Proliferative Stage: Involves the regeneration of the uterus ling and development of the egg in the ovary.
- Pituitary release follicle stimulating hormone, causes formation of a new graafian follicles in the ovaries.
- As follicles increase = oestrogen increase = FSH decrease. This is know as negative feedback.
- Usually only one follicle fully develops as it becomes dominant to all the others. Oestrogen from the dominant follicle inhibits FSH secretion.
- Oestrogen levels continue to increase, repairs endometrium and increases thickness.
- Oestrogen levels reach a critical level which causes the pituitary to release Lutinising Hormone.
- Ovulation
- Surge of LH = Ovulation; release of egg from ovary
- Causes graafian follicle to become corpus luteum
- Oestrogen levels decrease slightly
- Luteal Phase
- Corpus luteum secretes a smaller amount of oestrogen and progesterone, causes body temperature to increase slightly in the days following ovulation.
- High levels of progesterone create a negative feedback on FSH and no follicles develop in the ovaries.
- Progesterone maintains endometrium until theend of the cycle,to prepare for possible pregnancy.
- Towards the end of the luteal phase the corpus luteum degenerates which results in a decrease of progesterone and oestrogen levels.
- Inhibition on FSH is removed and the cycle begins again.
Menstrual Disorder
Fibroids: Benign tumours that grow in the muscular wall of the uterus
- Most common in women in their late reproductive years
- Can grow large and cause heavy menstrual bleeding
Treatment:
- Medication to reduce size and decrease pain
- Ultrasounds to break up tumours
- Surgical removal
- Severe: Whole uterus is removed - Hysterectomy
Copulation
Insertion of penis into vagina
Orgasm: Sexual arousal reaches maximum
Ejaculation: Release of semen from penis
Fertilisation
Sperm cell survival in reproductive tract = 3 days
Egg cell = 2 days
- Sperm is attracted to egg by chemotropisms
- Site of fertilisation = Fallopian tubes
- The fertile period is the time during the menstrual cycle where the female is most ikely to get pregnant. Around 5 days before ovulation and 2 days afterwards
Birth Control
Procedures taken to control the number of offspring produced
Abortion: Physical removal of a fetus from a uterus
Contraception: Intentional prevention of pregnancy by stopping fertilisation or implantation from occurring
- Natural Contraception
Avoiding sexual intercourse during the fertile period. Can be accurate by measuring female body temperature and vaginal discharge
- Mechanical Contraception
Barriers to the movement of sperm e.g. condoms, diaphragms and domes. Prevent entry of the sperm through the cervix
- Chemical Contraception
Use of spermocides and or hormones. E.g. The pill
- Surgical Contraception
Can only rarely be reversed, involves ligation (tying and cutting) of the fallopian tubes in females and of the sperm ducts in males (vasectomy).
Infertility
The inability to contribute to conception. A couple may be deemed infertile if ater 12 months of contraceptive free sexual intercourse they fail to conceive.
Male Infertility Causes
- Low sperm count
- Low sperm mobility
- Endocrine gland failure
Female Infertility Causes
- Fallopian tube blockage
- Endocrine gland failure
Treatment
Ranges from surgery to hormonal treatment. If these do not work IVF may be used.
Implantation and Placenta Formation
Implantation: Embedding of the embryo into the lining of the uterus
1) Fertilisation occurs
2) Diploid zygote divides by mitosis
3) Eventually enough mitosis has occurred for it to become a ball of undifferentiated cells called a morula; undifferentiated cells which form as a result of mitosis.
4) Morula is pushed down the fallopian tube by cilia.
5) Cells continue to divide until a fluid filled sack appears within the morula and is now called a Blastocyst; fluid filled sac containing an inner cell mass that gives rise to the embryo.
- It is now ready for implantation.
- At this stage the cells are undifferentiated and are referred to as stem cells
Implantation Occurs
- Outer layer of the blastocyst called a Trophoblast
1) The trophoblast layer embeds deeply into the endometrium by sending out long villi, these villi along with the mother's endometrial tissue give rise to the placenta
2) Inner cell mass continue to divide by mitosis and differentiate into various tissues to become organised into organ systems
- This occurs by the organisation of cells into 3 distinct layers
Ectoderm: Gives rise to skin and nervous system
Mesoderm: Gives rise to musculoskeletal system, kidneys, heart and lungs
Endoderm: Gives rise to the liver, pancreas and the inner lining of the digestive, breathing and excretory systems
3) A protective sac called an amnion forms around the embryo and is filled with amniotic fluid, functions in protection and shock absorption.
4) At the end of 8 weeks all the major organs have formed and the baby is now referred to as a feotus
In Vitro Fertilisation
Process of fertilising and egg cell with a sperm cell outside of the body usually in a petri dish to produce a diploid zygote that is implanted back into the uterus.
- Generally used for infertile couples
Childbirth
Process of moving the baby out of the uterus to form an independent individual
- Labour
- Amniotic sac around the baby bursts, caused by contractions of the uterus. These contractions are brought about by the hormone oxcytocin, which is secreted by the pituitary gland.
- Uterus contracts in waves that get more and more frequent as labour continues
- Contractions cause the cervix to dilate, once the cervix dilates the next stage occurs
- Parturition
- Process of the baby being born
- The cervix has dilated enough for the head to pass through, after the head the rest of the body comes out quickly
- The umbilical cord is clamped and cut
- Afterbirth
- Involves the passing of the placenta from the uterus
- Occurs due to the continued contractions of the uterus
Milk Production and Breast Feeding
Lactation: Production and secretion of milk by the breasts of the female
- Begins to occur in the days leading up to childbirth
- Response to the hormone prolactin, secreted after the levels of progesterone decrease
- Breast swell with milk and are considered an exocrine gland as they secrete their product into ducts
- After birth the breasts sectete a thick yellow substance called colostrum; nutritious and concentrated form of milk to protect the baby against disease in the first days of life.
Breast-feeding: feeding of a baby/infant directly from the breast
Advantages
- Contains all the correct nutrients in the correct proportions
- Contains antibodies to protect the baby against infections
- Correct temperature
- Does not pose any dangers to the child as it contains no pathogens
- Promotes strong bond between mother and baby
- Helps mothers' body recover quicker from the effects of pregnancy
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