Sexual reproduction in Plants Flashcards
What is the name for plants that have flowers?
Angiosperms.
What are the male spores of plants?
Pollen grains, produced in the anther.
What are the female spores of plants?
Embryo sacs, produced in the ovule in the ovary.
What is a hermaphrodite?
Flowers that contain both male and female parts.
How is a flower defined?
Four sets of modified leaved arising from a receptacle at the base.
What does the stamen (male part) consist of?
The anther and filament.
What does the carpel (female part) consist of?
The stigma, style, ovary, ovule and embryo sac.
What are sepals?
Found in the calyx, they are usually green and protect the flower in the bud.
What is the function of the nectary?
It releases sweet smelling nectar to attract pollinators.
What is the function of the filament?
It supports the anther and transports sucrose, minerals and water to the developing pollen grain.
What is the function of the anther?
It produces pollen grains.
What is the function of the stigma?
It is the receptive surface for the pollen grains.
What is the function of the style?
It supports the stigma.
What is the function of the ovary?
It produces embryo sacs.
Describe the features of insect-pollinated flowers
Colourful petals, sometimes with nectar guides
Scent and nectar
Anthers within the flower
Stigma within the flower
Small quantities of sticky, sculpted pollen
Produces larger pollen grains
Describe the features of wind-pollinated flowers
Petals absent or small, green and inconspicuous
No scent or nectar
Anthers hanging outside the flower
Large, feathery stigma hanging outside the flower
Large quantities of smooth pollen
Produces smaller pollen grains
What does the anther consist of?
Vascular strand, tapetum, pollen sac and a lateral groove.
What does a pollen grain consist of?
Exine, intine, generative and tube nucleus.
Describe pollen grain development
Each diploid mother cell undergoes meiosis, forming a tetrad of four haploid cells. Each haploid cell undergoes mitosis to produce two nuclei, a generative and a tube nucleus.
What is the function of the tapetum?
It provides nutrients and regulatory molecules to the developing pollen grains. It also forms the cell well, which is tough and resistant to chemical, desiccation resistant and resistant to mutation.
What happens when the pollen grain is mature?
The outer layers of the anther dry out, causing tension in the lateral groove. Dehiscence occurs in which the tension pulls the walls of the anther apart and the edges of the pollen sacs curl away. An opening called the stomium exposes the pollen grains and they are carried away by the wind.
Describe embryo sac development
In each ovule, a megaspore mother cell undergoes meiosis, making four haploid cells. Three disintegrate and the remaining cell undergoes three round of mitosis, producing eight haploid nuclei. These nuclei fuse to produce one haploid oosphere, three haploid antipodals, two haploid synergids and a diploid polar nucleus.
What does a mature embryo sac consist of?
One haploid oosphere, three haploid antipodals, two haploid synergids and a diploid polar nucleus.
What is pollination?
The transfer of pollen grains from the anther to the mature stigma of a plant of the same species.
What is self-pollination?
The pollen from the anthers of a flower is transferred to the mature stigma or the same flower of another flower of the same plant.
What is cross-pollination?
The pollen is transferred from the anthers of one flower to the mature stigma on another flower on another plant of the same species.
What are the advantages of self-pollination?
Inbreeding can preserve a successful genome that is suitable in a relatively stable environment.
What are the disadvantages of self-pollination?
There is a greater chance of two potentially harmful recessive alleles being brought together
Less genetic variation
What are the advantages of cross-pollination?
Outbreeding reduces the chance of producing harmful allele combinations
Outbreeding is of great evolutionary significance as in a particular environment, some genomes are more successful than others. It may allow species to survive in a changing environment
More genetic variation
What are the different methods employed to ensure cross-pollination?
Dichogamy- where the stamen and stigma ripen at different times
The anther being below the stigma so pollen cannot fall onto it
Genetic incompatibility
Separate male and female flowers on the same plant
Separate male and female plants
What is fertilisation?
The process by which a male gamete fuses with a female gamete to produce a zygote.
Describe the steps of double fertilisation
- When a compatible pollen grain lands on the stigma, it germinates in the sucrose solution secreted by the stigma and produces a pollen tube.
- The pollen tube nucleus is at the tip of the tube, with two male nuclei behind.
- The pollen tube grows out of the pollen grain through a gap in the cell wall and down the style, up a gradient of chemo attractants. The pollen tube nucleus uses hydrolases to digest the tissues of the style.
- The pollen tube grows through a gap in the integuments, the micropyle and passes into the embryo sac.
- The pollen tube nucleus disintegrates.
- The tip of the pollen tube opens, releasing two male gametes into the embryo sac.
- One of the male gametes fuses with the oosphere to form a diploid zygote.
- The other male gamete fuses with the diploid polar nucleus to make a triploid endosperm nucleus.
Describe the ovary in a plant
Nuclei in the embryo sac are surrounded by the nucellus, a layer of cells which provide nutrients. Around the nucellus are two layers of cells called integuments. A gap in the integuments is called the micropyle.
What does the diploid zygote become after fertilisation?
It divides by mitosis, becoming an embryo consisting of a plumule (shoot), a radicle (root) and one or two cotyledons (seed leaves).
What does the triploid endosperm nucleus become after fertilisation?
It develops into a food store, providing food for the developing embryo.
What do the outer integuments become after fertilisation?
They dry out, harden and become waterproof with deposits of lignin and become the seed coat or testa/
What does the micropyle become after fertilisation?
It remains as a pore in the seed.
What does the ovule become after fertilisation?
It becomes the seed.
What does the funicle become after fertilisation?
It becomes the funicle of the seed, attached at the hilum.
What does the ovary become after fertilisation?
It becomes the fruit.
Describe monocots
One cotyledon in seed
Leaf veins are parallel
Sepals, petals and stamens are in multiples of three
Vascular bundles scattered in roots
Vascular bundles scattered in stems
Give an example of a monocot
Maize.
Describe dicots
Two cotyledons in seed
Leaf veins form a network
Sepals, petals and stamens are in multiples of four or five
Vascular bundles in the centre of roots
Vascular bundles in a ring in stems
Give an example of a dicot
Broad bean.
What does dormant mean?
It describes a seed when its active growth is suspended as germination can only occur when specific conditions are met.
What is seed dispersal?
The movement of seeds away from the parent plant.
Why is seed dispersal neccassary?
If a seed were to germinate close to a parent plant, the parent plant would be more successful at obtaining water and minerals from the soil, and cast a shadow over the seedling, outcompeting it.
Describe and give an example of a plant with a wind dispersal method
Sails that allow wind dispersal, stiff parachute of hairs or pores. For example, a dandelion seed.
Describe and give an example of a plant with a transport dispersal method
Birds eat seeds that pass throw the digestive system and are dispersed in the faeces. For example, a song thrush eating berries.
Describe and give an example of a plant with a rolling dispersal method
When the fruit breaks open, the seed falls and rolls away from the parent tree. For example, a horse chestnut fruit.
Describe and give an example of a plant with a bursting dispersal method
When legume pods dry, they split and seeds scatter in all directions. For example, pea pods.
Describe and give an example of a plant with a water dispersal method
Seeds air cavities make them buoyant and able to float away. For example, a coconut palm.
Describe and give an example of a plant with a carrying dispersal method
Hooked seeds attach to animal coats and are carried away. For example, burdocks.
What are the different methods of seed dispersal?
Wind
Transport
Rolling
Bursting
Water
Carrying
What is the evolutionary advantage for a seed being able to go dormant?
Dormant seeds have a low metabolic rate, and so they survive very cold weather. The water content of a dormant seed is reduced below 10% and so seeds survive dry conditions.
What is the evolutionary advantage for methods of seed dispersal?
Seeds can be dispersed so they do not compete with the parent plant, and it allows the colonisation of new habitats.
How is the testa adapted?
It is chemically resistant so seeds survive adverse chemical conditions and it physically protects the embryo.
Why are inhibitors an evolutionary advantage for plants?
As they only allow germination at a suitable time of year. They are broken down in very cold weather in vernalisation so that the seed can germinate in the spring.
What is germination?
The process in which the plant grows from a seed. It begins with a very vigorous biochemical reaction and developmental activity and lasts until the first photosynthesising leaves are produced.
What are the requirements for successful germination?
A suitable temperature- the optimum temperature is the optimum for the enzymes involved, usually 5-30C
Water- to mobilise enzymes, for transport in the xylem and phloem and to vacuolate cells, making them turgid.
Oxygen- aeroibc respiration releases energy, which fuels metabolism and growth.
Describe the process of germination
When conditions are suitable, water is imbibed by the micropyle. Water causes the tissues to swell and provides suitable conditions for enzyme activity. Food reserves are broken down into soluble molecules, with the soluble products being transported to the embryo and carried in the phloem to the apical meristems. The swollen tissues rupture the testa and the radicle emerges from the seed. It is positively geotrophic and negatively phototrophic so grows downwards. Then the plumule emerges which is negatively geotrophic and positively phototrophic so grows upwards. When the plumule emerges from the soil, it straightens out and the leaves begin to unfurl and photosynthesise.
What macromolecules are involved in germination and how are they used?
Starch, hydrolysed by amylase into maltose is converted to cellulose for cell wall synthesis and for energy release.
Proteins, hydrolysed by protease into amino acids are used to synthesise new proteins and for energy release.
Why does the plumule emerge as a hook shape?
To prevent damage by soil abrasion.
What are the apical meristems?
Places where rapid cell division occurs.
When is germination complete?
As soon as the food reserves in the cotyledons have been depleted.
Describe the synthesis of sugars from gibberellic acid in the barley seed
- The seed secretes gibberellic acid which diffuses through the endosperm to the aluerone layer.
- The gibberellic acid switches on genes in the cells of the aleurone layer, resulting in transcription and translation, producing enzymes such as proteases and amylases.
- The proteases hydrolyse proteins in the aleurone layer to amino acids, which are used to make amylase and maltase.
- The carbohydrates diffuse out of the aleurone layer and hydrolyse the starch stored in endosperm cells.
- The sugars produced diffuse back through the endosperm to the plumule and radicle of the embryo.
- Sugars are respired for energy, which fuels biosynthesis and cell division bringing the seed out of dormancy.
