R2101 3.2 Describe the structure and functions of fruits and seeds Flashcards
What is fertilisation?
The fusion of the male gamete from pollen with a female gamete in the ovule to produce the embryo
The nucleus of the male gamete (pollen) joins with the nucleus of the female gamate (ovule)
What is a fruit?
- A fruit is formed from the ovary after fertilisation.
- In contain the seeds and occurs in a wide variety of forms
- Fruit is designed to help with seed dispersal
- The ovule becomes seeds, and the ovary wall swells to accomodate them as they develop.
- Can be fleshy, dry, edible or spikey
What is a seed?
A seed is formed from the ovule after fertilisation
How many gametes does the male nucleus have?
Two
What is the function of each male gamete?
- One gamate travels down the pollen tube to fuse with the female gamete to form a zygote. Further development and cell division takes place and the zygote becomes an embryo - the basis of a new plant within a seed.
- In many plants the second gamate fues with other cells in the ovule to form a food store for the developing seed - the endosperm
What are pseudocarps?
False fruits that form from other parts of the flower, not the ovary
Main fruit types (3)
- Dry:
Dehiscent (seed case splits)
Indehiscent / hard (seed case remains intact) - Fleshy or succulent
Succulent or fleshy fruits
- Includes those that are typically eaten - apples, pears, cherries, tomatoes, cucumbers etc
- Often have chemicals that prevent seeds germinating until all fruit pulp has been removed
e.g. elderberry passed through the gut of a bird and pulp is disgested. Seed is then excreted far from the original plant with its own fertiliser package
Succulent or fleshy fruits (2)
- Includes those that are typically eaten - apples, pears, cherries, tomatoes, cucumbers etc
- Often have chemicals that prevent seeds germinating until all fruit pulp has been removed
e.g. elderberry passed through the gut of a bird and pulp is disgested. Seed is then excreted far from the original plant with its own fertiliser package
Indehiscent dry fruits (3)
- Nuts like hazel, sweet chesnut
- Seeds like sunflower
- Winged samaras like sycamore and ash
Dehiscent fruits (2)
- Seedcase of delphiniums , poppies split and release dry seed cases
- Seed may be propelled a long way by the drying and twisting action of the seed pod
What is the function of a fruit? (2)
- The distribution and protection of the seed
- In may impose dormancy
What is the function of the seed? (3)
- The distribution and protection of the embryo
- In may impose dormancy
- It gives rise to new plants
How are seeds dispersed? (4)
- Wind
- Water
- Explosive
- Animals
Wind seed dispersal + examples (3)
- By censer mechanism (use of wind - swaying seeds escape out of pores) e.g. Papaver rhoeas
- Surface area maybe increased byvarious means to allow the seed to be carried long distances by the wind, like the winged seeds e.g. Tilia cordata
- Some plants use parachutes or silky tufts e.g. Taraxacum officinale
Water seed dispersal (3)
- Relatively rare
- Cocos nucifera float on ocean currents before being washed up on a beach to germinate
- Coconut has a fibrous outer layer that help it float