Flashcards in Sexual reproduction in plants Deck (35):
What are the petals?
Large and colourful in insect pollinated and small+green in wind pollinated.
What is the corolla?
A collective term for all petals (a whorl).
What is the sepal?
Small green leaf-like structure which protect the flower when in the bud.
What is the calyx?
A collective term for all the sepals.
What is the receptacle?
The swollen base of a flower, all flower parts are attached to.
What does the male stamen consist of?
The anther and filament.
What is the anther?
Produces pollen, has 4 pollen sacs, when mature sacs split and release it.
What is the filament?
Contains vascular tissue to support anther, transports sucrose and amino acids for formation of pollen grains.
Formation of pollen sacs?
An anther contains 4 pollen sacs, each one enclosed by protective fibrous layer. Inside layer is the tapetum (food store of energy for cell division).
Formation of male gametes?
Each pollen sac undergoes meiosis I and II to form a tetrad (micro spores).
Develop into pollen grains, undergo mitosis to produce generative and tube nucleus.
Generative divide to form 2 male gametes.
When pollen mature, anther dry and split, called dehiscence and release grains.
What is the female reproductive organ made up of?
The carpel, stigma and ovary with ovules inside.
What is the carpel?
It consists of the stigma, style and ovary.
What is the stigma?
Receives the pollen from the anther.
What is the ovary?
Contains the ovules, fertilised ovary becomes a fruit. ( Each ovule contains a female gamete- egg, becomes seed).
What is the structure of the ovule?
Each ovary contains one or more. 2 walls of ovule are integuments.
Ovule has small opening called micropyle, where pollen tube enters.
(Nucellus contains cells that provide butrients for growth and on diplod cell 2n).
Formation of the female gamete?
The diploid cell divides by meiosis to form 4 haploid cells (megaspores), three degenerate and one survives (n), grows to form the embryo sac. The nucleus undergoes 3 divisions, 8 haploid nuclei formed. One near micropyle is egg cell.
Two nuclei in middle of sac are called polar nuclei.
What is pollination?
Pollination is the transfer of pollen from the anther of one plant to the stigma of another.
How are insect-pollinated plants adapted?
Nectar and a scent present.
Sticky stigma to collect pollen.
Brightly coloured petals.
Anthers positioned to rub pollen onto insects.
Pollen grains have barbs for hooking onto insect fur.
How are wind-pollinated flowers planted?
Pollen grains very small and light, larger numbers of.
Petals are small and green, no need to attract insects.
NO scent or nectary.
Stigma are feathery to catch pollen in wind.
Anthers are exposed to wind so pollen can be blown away.
What is cross pollination?
When pollen is transferred from the anther of one flower to the stigma of a different flower.
What is self-pollination?
When pollen is transferred from an anther of one flower to the stigma of the same flower.
Advantages of self pollination?
It can give some genetic variation if cross pollination is not possible.
Disadvantages of self pollination?
Self-pollination reduces genetic variation.
There is a greater chance of two undesirable recessive alleles being brought together.
First part of fertilisation?
Pollen grain land on stigma (of same species), stigma produces sugary solution, where the grain germinates, producing pollen tube.
Tube secretes enzymes, which digest through tissue of style.
Generative nucleus divides by mitosis to produce 2 male gametes (n).
Second part of fertilisation?
Tube reaches ovary, enters ovule through micropyle. Tube nucleus disintegrates and the tip of tube bursts, 2 male gametes released into embryo sac.
One fuses with female gamete to form a zygote (2n)
Other one fuses with both polar nuclei at centre of embryo sac to form a triploid endosperm nucleus. Called double fertilisation, zygote develops into embryo plant, grows into a new plant.
Function of the tube nucleus?
Controls the growth of the pollen tube.
How does the ovary develop into a fruit?
Water leaves the seed, it dehydrated and therefore all metabolic reaction stop. The seed is said to become dormant. The ovary develops to become a fruit.
What are monocotyledons?
(e.g. cereals, maizes) they are plants that have seeds with only one cotyledon (seed leaf).
What are dicotyledons?
(e.g. broad beans), these plants have seeds with two cotyledons (seed leaves).
What are the parts of the seed?
The embryo is the essential part; radicle develops into root and plumule develops into shoot. 1 or 2 cotyldeons, grow from hypocotyl, may be taken above the ground during germination.
A food store supplies the embryo and growing plant until it can make own by photosynthesis. The store may be either cotyledon or in endosperm. The testa is the tough protective outer covering the seed.
About monocotyledon fruit?
E.g. Sweetcorn is a fruit as the ovary wall surrounds seed coat and seed.
Embryo plant has 1 cotyledon.
Endosperm is retained and once the seed germinates, the small cotyledons channels sugars to the growing tip.
What are the conditions needed for germination?
Water- nutrients in dry seed need to re hydrated before use, it cracks testa so roots can grow and activates enzymes.
Oxygen- Aerobic respiration for germination, lots of ATP for growth needed.
Temperature- optimum temp for germination is the optimum for enzymes to work, different for all seeds (times of year).
How does seed germination happen?
Water enters through micropyle so embryo synthesises amylase. Water softens testa to allow it to split. Embryo releases amylase which hydrolyses starch in cotyledons into maltose. Maltose is absorbed by embryo. Maltose in embryo broken into glucose and used in respiration for energy and growth.
Part two of seed germination?
Testa ruptures as radicle grows out. Radicle grows down and plumule (shoot) grows up. Cotyledons below ground use starch for growth. Plumule is bent over and pushes through soil, protects tip from being damaged. When emerges it unfolds and begins to make food through photosynthesis.