3) Reproduction and inheritance Flashcards
Purpose of pollination
-plants produce pollen, which contains a nucleus inside that is the male gamete - not capable of moving from one place to another
-so plants have mechanisms to transfer pollen from the anther (male part of the flower) to the stigma (female part of the flower) - pollination
Two main mechanisms of pollination
-where pollen is transferred by insects (or sometimes birds or bats)
-where pollen is transferred by the wind
Structure of a typical flower
-Sepal - Protects unopened flower
-Petals - Brightly coloured to attract insects
-Anther - Produces and releases the male sex cell (pollen grain)
-Stigma - Top of the female part of the flower which collects pollen grains
-Ovary - Produces the female sex cell (ovum)
-Ovule - Contains the female sex cells (found inside the ovary)
Process of insect pollinating flower
- insects often visit flowers to collect nectar
-sugary substance produced by insect-pollinated flowers at the base of their petals which provides insects with energy - as an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect’s body
- when the insect visits another flower, it may brush against the stigma of the second flower and deposit some of the pollen from the first flower
Adaptations of insect pollinating flowers
-Scent and Nectar - Entices insects to visit the flower and push past stamen (anther+filament) to get to nectar
-Number of pollen grains - Moderate - insects transfer pollen grain efficiently with a high chance of successful pollination
-Pollen grains - Larger, sticky and/ or spiky to attach to insects and be carried away
-Anther - Inside flower, stiff and firmly attached to brush against insects
-Stigma - Inside flower, sticky so pollen grains stick to it when an insect brushes past
Wind pollinated flower adaptations
-Petals - Small, dull, often green or brown in colour
-Scent and Nectar - Absent - no need to waste energy producing these as no need to attract insects
-Number of pollen grains - Large amounts - most pollen grains are not transferred to another flower, so the more produced, the better the chance of some successful pollination occurring
-Pollen grains -Smooth, small and light so they are easily blown by the wind
-Anthers - Outside flower, swinging loose on long filaments to release pollen grains easily
-Stigma - Outside flower, feathery to catch drifting pollen grains
Two types of pollination
-cross pollination
-self pollination
Cross pollination
-occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
-most plants do this as it increases the genetic variation in the offspring
Self pollination
-occasionally, the pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant - reduces genetic variation in the offspring as all gametes come from the same parents and are genetically identical
-can be a disadvantage if environmental conditions change as it is less likely that any offspring will have adaptations that suit the new conditions
Fertilisation in plants
Fertilization occurs when the pollen grain nucleus fuses with the ovum nucleus
Process of fertilisation in plants
- in order to reach the ovum nucleus, the pollen grain grows a pollen tube
-only happens if the pollen grain has landed on the right kind of stigma - the nucleus inside the pollen grain moves down the tube as the tube grows down the style towards the ovary
- once the nucleus of the pollen grain and nucleus of the ovum have fused, that particular ovule has been fertilized and a zygote has been formed
-the zygote will then start to divide
Seed and fruit formation
- after fertilization, the ovule (that contains the zygote) develops into the seed
- the wall of the ovule develops into the seed coat - testa
- parts of the flower surrounding the ovule (mainly the ovary walls) develop into the fruit, which contains the seeds
Fruits - seed dispersal
-The fruit provides a mechanism for seed dispersal (getting the seeds away from the parent plant)
-Some fruits are eaten by animals, which then disperse the seeds in their droppings (the tough outer coat of seeds stops them from being digested)
-Some other fruits have sticky hooks that get caught in the fur of passing animals
Germination process
-start of growth in the seed - seed contains the zygote which divides into cells that then develop into the embryo plant
1. Cotyledon (first part of plant that emerges) surrounds the embryo
-contain food reserves that supply the seedling with food (energy for growth) until it grows its own leaves, makes its own food via photosynthesis
2. after taking in water, the seed coat splits
3. leads to the production of the plumule (first emerging shoot) and radicle (first emerging root)
Conditions of germination
Water:
-allows seed to swell up, causes the seed coat to burst
-allows growing embryo plant to exit the seed
-water allows the enzymes in the embryo to start working so growth can occur
Oxygen:
-required for respiration, so energy can be released for germination
Warmth:
-germination improves as temperature rises (up to a certain point)
-reactions controlled by enzymes
-cannot function effectively when temperatures are too low
Investigating conditions for germination
- Set up 4 test tubes, with each containing 10 cress seeds on cotton wool
- Label the test tubes A, B, C and D
A: leave the cotton wool dry
B: add enough water to the cotton wool so that it becomes moist
C: add enough water to cover the cotton wool and seeds, then carefully add a layer of oil on top of the water
D: add enough water to the cotton wool so that it becomes moist - Leave tubes A, B and C at room temperature or incubated at a specific temperature (e.g. 20°C)
- Place tube D in a fridge (approximately 4°C)
- Leave all tubes for a set period of time (e.g. 3 - 5 days)
-Ensure the cotton wool in tubes B and D remains moist throughout this time by adding more drops of water if required - Compare the results and see which tube has the greatest number of germinated seeds
Asexual reproduction in plants
-only involves one parent and all offspring produced are exact genetic copies of each other and the parent plant - clones
-can occur naturally or artificially
-plants: runners, cuttings
Natural asexual reproduction - runners
- Runners are horizontal stems that grow sideways out of the parent plant, and have small plantlets at their ends
- Once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant
Artificial asexual reproduction - cuttings
- Gardeners take cuttings from good parent plants
- This cutting can either be placed into water until new roots grow or can sometimes be placed directly into soil
- Sometimes, the stem of the cutting may first be dipped into ‘rooting powder’, which contains plant growth regulators (rooting hormones) that encourage new root growth
- These cuttings are then planted and eventually grow into adult plants that are genetically identical to the original plant
- Plants cloned by taking cuttings can be produced cheaply and quickly
Human male reproductive system structures
-prostate gland
-sperm duct
-urethra
-testes
-scrotum
-penis
Prostate gland function
Produces fluid called semen that provide sperm cells with nutrients
Sperm duct function
Sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation
Male reproductive system - Urethra function
Tube running down the centre of the penis that can carry out urine or semen, a ring of muscle in the urethra keeps the urine and semen separate
Testes function
Contained in a bag of skin (scrotum) and produces sperm and testosterone
Scrotum function
Sac supporting the testes outside the body to ensure sperm are kept at temperature slightly lower than body temperature
Penis function
-Passes urine out of the body from the bladder
-allows semen to pass into the vagina of a woman during sexual intercourse
Human female reproductive system structures
-oviduct
-ovary
-uterus
-cervix
-vagina
Oviduct function
Connects the ovary to the uterus and is lined with ciliated cells to push the released ovum down it
Ovary function
Contains ova (female gametes) which will mature and develop when hormones are released
Uterus function
Muscular bag with a soft lining where the fertilized egg (zygote) will be implanted to develop into a fetus
Cervix function
Ring of muscle at the lower end of the uterus to keep the developing fetus in place during pregnancy
Vagina function
Muscular tube that leads to the inside of the woman’s body, where the male’s penis will enter during sexual intercourse and sperm are deposited
Adaptation of sperm cells
Has a flagellum:
-Enables it to swim to the egg
Contains enzymes in the head region (acrosome):
-To digest through the jelly coat and cell membrane of an egg cell when it meets one
Contains many mitochondria:
-Provide energy from respiration so that the flagellum can move back and forth for locomotion
Adaptation of egg cell
Cytoplasm containing a store of energy:
-Provides energy for the dividing zygote after fertilisation
Jelly like coating that changes after fertilisation:
-Forms an impenetrable barrier (fertilisation membrane) after fertilisation to prevent other sperm nuclei entering the egg cell
Sperm vs egg size
Sperm: small
Egg: large
Sperm vs egg motility
Sperm: Capable of locomotion
Egg: Not capable of locomotion
Sperm vs egg numbers
Sperm: produced every day in huge numbers (around 100 million per day)
Egg: Thousands of immature eggs in each ovary, but only one released each month.
Human fertilisation process
- Ejaculation, semen into vagina of female
- Sperm cells follow chemical trail, travel through plug of mucus in cervix, reach uterus
- Into oviduct, meet egg cell
- Head releases enzymes that digest path through protective outer layer of egg cell
- Egg cell releases thick layer of material, prevents any more sperm cells from entering
- Male, female gametes fuse, become zygote (fertilised egg cell)
