Reproduction in Plants (S) Flashcards
What is the function of the flower
Sexual reproduction
Sexual reproduction
involves fusion of gametes from both parents
Carpel
Female reproductive organ
- Stigma
- Style
- Ovary
Stamen
Male reproductive organ
- Anther
- Filament
Function of sepals
Protect the flower when in the bud
Function of petals
Attract animals
Function of stigma
Traps pollen
Function of style
Collects pollen
Function of ovary
Fertilisation becomes the fruit
Function of Anther
Pollen production and release
Function of Filament
Holds anther to release pollen
Function of Nectary
Produces nectar
Function of Receptacle
Floral parts arise from the receptacle
Female organ
- Stigma, style, ovary
- Egg cell (n)
- 2 polar nuclei (n,n)
- Collectively called 2 female gametes
How is the embryo sac formed?
- Megaspore (mother cell) 2n divides by meiosis
- Four haploid megaspores are formed (n)
- 3 megaspores degenerate
- Nucleus of the surviving megaspore divides by mitosis 3 times
- Single-cell with eight nuclei is called the embryo sac
- One nucleus develops the egg cell
- Two nuclei become the polar nuclei
- Female gametes are formed by meiosis followed by mitosis
What is produced by each fertilisation
- Zygote
- Triploid endosperm nucleus
Male reproductive organ
Stamen
- consists of anther and filament
- Each pollen grain contains 2 male gametes
Outline how Pollen Grain is formed
- Microspore mother cell (2n) divides by meiosis
- produced 4 haploid cells which stick together to form a (tetrad)
- Nucleus of each microspore (pollen grain) divides by mitosis
- Forming tube and generative nucleus
- Generative nucleus divides by mitosis forming the 2 male gametes, which appear as 2 nuclei
The mature pollen grain is surrounded by 2 walls
- Tough outer exine
- Inner exine
Pollination
Transfer of pollen from the anther to the stigma
Self Pollination
Is formed when pollen is transferred from the anther to the stigma of the same flower to another flower
- occurs in cereal crops
-
Mechanism to prevent self-pollination
Carpel matures first so the plant can release its own pollen
Cross-Pollination
Pollen from the anther of one plant to the stigma of another plant of the same species
Mechanisms that prevent self-pollination
Greater variation
Name 2 methods of cross-pollination
- Animals
- Wind
Methods of pollination in the flower
Animal: nectar to attract
Wind: Small
Methods of pollination in the pollen
Animal: large and sticky to attach to insects body
Wind: Small and dry which is easy to carry
Methods of pollination in the stigmas
Animal: sticky which forces insects to forage
Wind: Feathery which increases the surface area
Methods of pollination in the anthers
Animals: small inside flower which forces insect to forage
Wind: Large, outside flower which is an easy release of pollen
Hay fever
- allergic reaction to inhaled allergens (pollen, dust)
Symptoms of hay fever
- Inflammation of mucous
- blocked nose
Treatment for hay fever
- Anti-histamines
- Decongestant to clear nasal
Define Fertilisation
- Fusion of the male gamete with the female gamete to form a diploid zygote
Give an account for the lead up to double fertilisation
- Pollen grains are transferred to stigma during pollination
- Generative nucleus divides by mitosis forming the 2 male gametes
- Pollen grain absorbs water and germinates to produce a pollen tube
- The tube nucleus and the 2 male gametes move down into this pollen tube
- The pollen tube grows down through the style and ovary tissue towards the embryo sac by the presence of chemotropism
- The tube nucleus at the tip of the pollen tube controls and directs its growth
- On reaching the micropyle, the pollen tube enters the embryo sac after which the tube nucleus degenerates
Outline what occurs during double fertilisation
- 2 haploids make gametes enter the inside of the embryo sac where double-fertilisation occurs
- One male gamete fuses with the egg cell forming a diploid zygote
- A second male gamete fuses with the two polar nuclei to form a triploid endosperm nucleus
Events following fertilisation
- Ovule becomes the seed
- Integuments become the testa
- Ovary becomes the fruit
- Ovary wall becomes the fruit wall
What is testa
A tough hard seed that protects the seed
What is Helium
A scar is attached to the ovary wall
What is Micropyle
A pore
Radicle develops into
Develops into root
Plumule develops into
Develops into shoot
What are cotyledons
Seed leaves formed by some of the embryo cells
They contain food reserves that are used in the early stage of germination
They secrete enzymes that digest endosperm food, absorb it and pass it on to the developing embryo
Describe dicotyledonous seeds
- 2 seed leaves
- Non-endospermic seeds
- Food store needed by the developing embryo is in the cotyledons
- Biomolecules stored include lipids and proteins
- Eg: Broad Bean
Describe Monocotoledonous seeds
- 1 seed leaf
- Seeds are endospermic
- Food store needed by the developing embryo in the endospore
- Biomolecules stored include lipids and proteins
- Eg: Maize (not a typical monocot, stores its food in the cotyledon)
Fruit formation
Fertilised ovary becomes the fruit
Fruit formation is stimulated by
The release of auxin
Fruit functions include…
- To aid seed dispersal
- Protect seeds
What is a false fruit
Do not develop from the ovary, but from other floral parts
eg: strawberries
Seedless fruits are produced by
- Spraying flowers with auxins, before pollination and fertilisation
- Breeding programmes
What is meant by seed dispersal
Scattering of seeds away from the parent plant
Advantages of seed dispersal
- Reduces competition
- Colonisation of favourable habitats
- Better survival rate
Seed dispersal methods
- Wind
- Animals
- Water
- Self dispersal
How are seeds dispersed by the wind?
seeds are light and easier to disperse by the wind
eg: Dandelion
How are seeds dispersed by an animal?
Burdock clings to animal hair
Seeds egested
How are seeds dispersed by Water?
Floating on rivers or streams
eg: water lily
How are seeds dispersed by self dispersal?
Open scattering seeds under pressure
eg: peas