Topic 16 Flashcards
Asexual reproduction
Process used to produce genetically identical offspring from one parent
. Example: strawberry plants using runners, tulips using bulbs and bacteria by splitting in two
Asexual reproduction advantages
- Lots of offspring can be prodcuced very quickly
- Less energy required
- Offspring are genetically identical -> beneficial features will be inherited
- Offspring reach maturity quicker
Asexual reproduction disadvantages
- No genetic variation -> unlikely to adapt to changes in the environment
- Overpopulation
Sexual reproduction
Process used to produce offspring that are genetically distinct from each other -> involves the fusion of the nuclei of two gametes, which are haploids (fertilisation) to form a zygote, which is diploid
Sexual reproduction advantages
- Genetic variation -> likely to adapt to changes in the environment
- Diversity can lead to natural selection and evolution
- Selective breeding can be used to improve crop production and quality
Sexual reproduction disadvantages
- Takes more time and energy than sexual reproduction
- Two parents are needed
Stamen
Produces male gametes -> consits of anther and filament
Anther
Contains pollen grains which produce male gametes
Filament
Holds up anther
Petals
Brightly colored in insect-pollinated flowers to attract insects for pollination
Sepals
Protect flower in bud
Carpel
Produces female gametes -> consist of stigma, style and ovary
Stigma
End bit that pollen grains attatch to
Style
Supports stigma and connects it to ovary
Sexual reproduction in plants
Plants that reproduce sexually have both male and femal gametes in flower
Pollination
Transfer of pollen from an anther to a stigma
Self-pollination
Self-pollination: pollen is transferred from anther to a stigma on either same flower or a different flower on same plant
. Don’t rely on pollinators -> easier for them to spread to locations where there’s no pollinators
. Produces less variation (gene pool smaller) -> less likely to adapt to stimuli in environment
Cross-pollination
Pollen is transferred from anther to stigma on a flower from a different plant of same species
. Rely on pollinators to transfer pollen grains elsewhere -> If pollinator population declines = harder for flowers to reproduce
. Produces more variation -> more likely to adapt to stimuli in environment
Plant pollination: adaptations for insect pollination
. Large, brightly coloured petals to attract insects
. Scented flowers and nectaries (glands that secrete nectar) to attract insects
. Sticky stigma so pollen picked up by insects on other plants will stick to stigma
. Make big, sticky pollen grains which stick to insects as they go from plant to plant
Plant pollination: adaptations for wind pollination
. Small, dull petals
. No nectaries or strong scents
. Long filaments that hand anthers outside of flower so a lot of pollen fets blown away by wind
. Large and feathery stigma which hangs outside flower to catch pollen as it’s carried past by wind
Fertilisation in plants
Nucleus from pollen grain (male gamete) fuses with nucleus of female gamete in ovule -> happens in ovule
Steps of fertilisation in plants
- Pollen grains lands on stigma of flower -> with help from insects or wind
- Pollen tube grows out of a pollen grain and down through style to ovary and into ovule
- A nucleus from male gamete moves down tube to join with a female gamete in ovule and fertilisation occurs forming a zygote -> zygote divides by mitosis to form an embryo
- Each ovule containing fertilised female gamete forms a seed, which can grow into a new plant
Germination
After a seed is formed it will often lie dormant until conditions around it are right for germination (growth into a plant)
. Water: to activate enzymes that break down food reserves in seed
. Oxygen: for respiration -> transfers energy from food to growth
. Suitable temperature: for enzymes inside seed to work -> depends on type of seed
Urethra
Tube that carries sperm through penis during ejaculation and urine also passes through it to exit body
Prostate gland
Produces liquid that’s added to sperm to make semen
Penis
Swells when filled with blood for introducing sperm into female
Testis
Where sperm is made
Sperm duct
Muscular tube that carries sperm from testis towards urethra
Scrotum
Hangs behind penis and contains testes
Oviduct
Muscular tube that carries the ovum (egg) from ovary to uterus and where fertilisation happens
Uterus
Organ where embryo geows
Vagina
Where sperm are deposited
Cervix
Neck of uterus
Ovary
Organ that produces ova and sex hormones
Egg cells: Energy stores in cytoplasm and Jelly coating
. Energy stores in cytoplasm: provide nutriens for zygote so it can divide after fertilisation to form and embryo
. Jelly coating: after fertilisation it changes structure to stop any more sperm from getting in -> make sure offspring end up woth right amount of DNA
Sperm cells: flagellum, acrosome and mitochondria
. Flagellum: to swim towards egg
. Acrosome: portion in head with enzymes that digest a way through jelly coat of egg cell
. Mitochondria: provide energy for flagellum to move
Egg VS sperm cell: size
Egg cell: About 0.1 mm in diameter
Sperm cell: About 0.05 mm in length
Egg VS sperm cell: structure
Egg cell: spherical -> lots of cytoplasm surrounded by jelly coating
Sperm cell: Head and flagellum -> small amount of cytoplasm
Egg VS sperm cell: mobility
Egg cell: don’t move independently
Sperm cell: able to move due to presence of flagellum
Egg VS sperm cell: numbers
Egg cell: About 300,000 present at puberty -> released one at a time each month
Sperm cell: millions produced + released everyday
Fertilisation
Fusion of nuclei from male gamete (sperm) and female gamete (egg cell)
Pregnancy: early development
Zygote forms embryo (ball of cells) that implants into lining of uterus
Pregnancy: umbilical chord
Carries substances between fetus and placenta
Pregnancy: placenta
- Allows dissolved nutrients and dissolved oxygen to pass into fetus’s blood from mother’s blood
- Allows excretory products to diffuse in opposite direction
- Provides barrier between most toxing and pathogens -> some toxins and pathogens can still enter placenta and affect fetus
Pregnancy: aminotic fluid
Aminiotic sac -> contains aminiotic fluid
- Protects fetus against knocks and bumps
- Supports fetus as it grows
- Allows fetus to move
Hormones in puberty: testosterone
. Extra hair on face and body
. Muscles to develop
. Penis and testes enlarge
. Sperm production
. Deepening of voice
Hormones in puberty: oestrogen
. Extra hair on underarms and pubic area
. Hips to widen
. Development of breasts
. Egg release and start of periods
Stages of the menstrual cycle
Stage 1: (day 1-4) menstruation starts -> uterus lining breaks down for about 4 days
Stage 2: (day 4-14) uterus lining builds up into thick spongy layer full of blood vessels + follicle (egg and its surrounding cells) matures in one of ovaries
Stage 3: (day 14) ovulation occurs -> egg released from follicle
Stage 4: (day 14-28) remains of follicle develop into corpus luteum + uterus lining is maintained -> if no fertilised egg is present and implanted the lining starts to break down and cycle starts again
Hormones in menstrual cycle: FSH
. Causes follicle to mature in one of ovaries
. Stimulates ovaries to produce oestrogen
Hormones in menstrual cycle: oestrogen
. Produced in ovaries
. Causes lining of uterus to grow
. Stimulates release of LH (causing release of an egg) and stops release of FSH
Hormones in menstrual cycle: LH
. Stimulates release of egg from follicle (ovulation) at day 14
. Stimulates remains of follicle to develop into corpus luteum -> secretes progestrone
Hormones in menstrual cycle: progestrone
. Produced in ovaries by corpus luteum after ovulation
. Prepares uterus to receive fertilised egg by mantaining uterus lining during second half of cycle -> when level of progestrone drops the uterus lining breaks down
. Stops release of FSH and LH
Hormones in pregnancy: FSH and LH
Inactive durimg pregnancy
Hormones in pregnancy: oestrogen and progestrone
Produced in placenta (progesterone also in smaller amount in ovaries)
- Levels stay high during pregnancy:
. To stimulate breast growth
. To mantain uterus lining
. Development of milk ducts
STI (sexually transmitted infection)
Infection that is transmitted throgh sexual contact -> caused by a pathogen
HIV (human immunodeficiency virus)
Pathogen that causes and STI
- Can lead to aids:
. Immune system deteriorates and eventually fails
. Vulnerable ro illness
How can HIV spread
HIV is spread via bloodily fluids bith sexually and non-sexually:
. Sexual contact
. Sharing needles
. Pregnancy
. Breastfeeding
. Childbirth
Controlling spread of STIs
. Education and awarness of STIs
. Abstinence -> not having sexual intercourse
. Use of condom
. Limiting number of sexual partners
. Medication
