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
Animal seed dispersal + examples (3)
- Attachment - hooked fruit such as such as burdock (Arctium tomentosum) attached themselves to animals or gardeners
- Scatter hoarding - nuts such as acorns (Quercus robur), hazelnuts (Corylus avellana) dispersed by rodents
- Frugivory - Succulent seeds and fruits eaten by birds. Such as hawthorn (Crataegus monogyna) and cherries (Prunus avium)
Explosive dispersal + examples
- Fruit splits open propelling seed into the air e.g Cardamine hirsuta (Hairy bittercress)
- Tensions setup by unequal drying of the seedcase causes pods of legumes to split along one side e.g. Pisum sativum
Main parts of a seed (3)
- An embryo or immature plant
- Food store to fuel growth
- Protective outer coat
What is germination?
Is the growth of a plant from its seed to it appearance above ground
What is dormancy?
Period of reduced metabolic activity in the plant
What is seed viability?
Whether or not the seeed has the capacity to grow - is it live
What is quiescence?
Resting period while the seed waits through winter for a suitable growing period
Food storage in seeds (2)
- In cotyledons
- In endosperm (many monocots)
Parts of a dicot seed (9)
- Embryo
- Plumule
- Epicotyl
- Cotyledon
- Hypocotyl
- Radicle
- Testa
- Hilum
- Micropyte
What is the testa? (4)
- The protective seed coat. Waterproof and air tight
- Very tough and may need to be damaged before germination takes place
- Formed from integuments surrounding the ovule
- May contain germination inhibators which enable seeds to stay dormant over winter
What is the cotyledon? (2)
- Seed leaf that provides a store of food for the germinating leaf
- May be one or two
What is the plumule
The part of the seed that will become the first shoot
What is the radicle
The part of the seed that will become the first root
What is the hilum
The point where the seed was attached within the ovary
What is the micropyle? (2)
- A small hole in the testa where the pollen tube entered the ovule at the time of fertilisation
- Sometimes water can enter here to trigger germination
What is the Hypocotyl (2)
- Between the cotyledons and root
- Connects the plumule to the radical
What is the epicotyl?
1.Between the plumule and radicle, this lies above the cotyledons and gives rise to the stem.
Parts of the embryo (5)
- Plumule
- Epicotyl
- Cotyledon
- Hypocotyl
- Radicle
What is the Coleoptile? (2)
- Monocots only
- Sheath that protects the plumule on its emergence from the soil
What is the Coleorhiza (2)
- Monocots only
- Sheath like structure that protects the radicle and connects to the coleoptile
Dormancy details (4)
(Not seeds)
- Perennial and biennial plants cope with winter cold by slowing down their metabolisms.
- Growth above ground dies back in herbaceous plants
- Leaves are shed by deciduous trees and shrubs
- In evergreens growth slows
Process of germination (6)
- Seed starts to take up water through micropyle (imbibition)
- Respiration rates rise as cells start to grow and divide
- Once cells have taken in water the embryo grows by cell division
- First root develops and radicle is pushed through the seed coat to anchor the seedling as it develops and take in water and minerals from the soil.
- Next the shoot develops - the plumule emerges from the seed as it splits
- Plumule develops into whole plant
What is epigeal germination? (3)
- The hypocotyl below the cotyledons grows upward through the soil pulling the cotyledons and plumule to the surface.
- The cotyledons unfurl as seed leaves. These start photosynthesising and the seeding is independant of its food reserves
- e.g. French bean Phaseolus vulgaris
What is hypogeal germination
- Where the epicotyl above the cotyledones elongates and pulls the plumule to the surface where the first true leaves grow.
- Cotyledones stay underground and evenntually decompose
- e.g. Broad bean Vicia faba
What is hypogeal germination
- Where the epicotyl above the cotyledones elongates and pulls the plumule to the surface where the first true leaves grow.
- Cotyledones stay underground and evenntually decompose
- e.g. Broad bean Vicia faba
What does a seed need to germinate? (3)
- Water
- Oxygen for respiration
- A temperature high enough to sustain growth
