knowledge organisers unit 4 Flashcards
(48 cards)
What organ is responsible for sexual reproduction in a plant
The flower. Gametes made, released and combine in the flower
What is pollination
The transfer of pollen to the stigma
What is the male gamete
Pollen
What is the female gamete
Ovule
What is self pollination
Pollen from plant transferred to the stigma of the same plant
What is cross pollination
Pollen from one plant transferred to the stigma of a different plant of the same species
What kind of variation occurs during self pollination
Only variation is mutation, independent assortment, and crossing over in meiosis of gamete formation
What kind of variation occurs in cross pollination
Variation from mutation, meiosis, and from having genetic material from 2 different parent plants
Advantages and disadvantages of self pollination
Successful plants in a stable environment, but species won’t be able to adapt to change
Advantages of cross pollination
Species more likely to survive a changing environment due to genetic variation
How can plants prevent self pollination
By having irregular flower structure e.g. different positioning of anther and stigmas or different ripening times
Carpel in insect pollinated flowers
Made of sticky stigma to collect pollen from insects.
Carpel in wind pollinated flowers
Large and feathery and hangs outside the flower
Stamen in insect pollinated flowers
Tucked inside flower so insect rubs past to pick up the pollen
Stamen in wind pollinated flowers
Large and hangs outside the flower
Where do pollen grains develop
In the anther
How do pollen mother cells develop
By mitosis
Why does meiosis occur in fertilisation of plants
To produce a tetrad of 4 haploid cells
What does mitotic division in the nucleus of haploid pollen grains form?
Forms a generative nucleus and tube nucleus
What does the tapetum do
Provide nutrients to developing pollen grains
How does the lateral groove occur
Tension in the lateral groove increases as the anther dries out. Dehiscence occurs when walls of pollen sac curl away, exposing pollen grains to wind and insects.
Formation of the ovule
- A megaspore mother cell carries out meiosis and 4 haploid nuclei are formed.
- 3 nuclei degenerate and 1 divides by mitosis three times to produce the 8 cells (3 antipodal, 2 polar nuclei, female gamete with 2 synergids)
Fertilisation steps
- pollen grain on compatible stigma produces hydrolase enzymes, forming a pollen tube leading to the micropyle of the embryo sac.
- Pollen tube formation under control of tube nucleus.
- Pollen tube growth is negatively aerotrophic and positively chemotrophic.
- One male gamete enters the embryo sac and fuses with the female gamete to produce a diploid zygote.
- Second male gamete fuses with the two polar nuclei to form a triploid primary endosperm nucleus.
How are seeds an adaptation to terrestrial life?
Can survive very dry conditions, have enough food store to provide food until the new plant can photosynthesise
