Sexual Reproduction In Flowering Plants Flashcards
Structure of a flower
Receptacle
- swelling at he base of a flower. It supports the flower
Sepals
- function is to protect the flower when it Is a bud
Petals
- protect the other parts of the flower sometimes attract insects
Stamens
- male part of the flower - The another produces pollen grains - The filament supports the anther
Carpels
- female part of the flower - stigma is the place where pollen lands - Style connects the stigma to the ovary - Contains one or more ovules, each ovule produces an egg
Formation Of male gametes
Anther composed of 4 pollen sacs
Each pollen sac is lined with an epidermis and a fibrous layer
Each pollen sac has a layer o diploid cells called microspore
These cells divide by meiosis to form a group of 4 pollen cells called a tetrad
The tetrad soon splits apart to form 4 individual pollen grains
The immature pollen grains are called microspores , each has a single haploid nucleus
The nucleus divides by mitosis to form to haploid nuclei
- one of these "Tube Nucleus" does not divide anymore - The second nucleus "Generative nucleus " divided by mitosis to form two sperm nuclei
The mature pollen grains form a though, patterned outer wall called the exine. The inner flexible wall of the pollen grain is called is called the intine
Pollen grains are formed inside the anther . When they are mature the anther breaks open and the walls of the pollen sacs fold back
Means pollen grains are exposed on the outside dif the anther
Formation of female gametes?
- each ovules has two walls called integuments . There’s a small opening in integuments called microphyle
The microphyle allows the pollen tube to enter the ovule
Most of the ovules consists of diploid nourishing cells called the nucellus
The megaspore Mother cell is a single diploid cell in the centre of the ovule
Cell divides by meiosis to form the embryo sac
3 of 4 haploid nuclei in embryo sac die
4th nucleus divides by mitosis 3 time stop form 8 haploid nuclei
One of these nuclei becomes the egg nucleus which forms the egg
Two more form the polar nuclei
The egg cell and two polar nuclei are female gametes
The carpel now appears
What is pollination?
“Pollination is the transfer of pollen from an anther to a carpel”
“Self- pollination” means that the anther and carpel are on the same plant :cereals, offspring weaker
“Cross-pollination” means that the anther and carpel are on different plants : stronger healthier offspring
Methods of cross- pollination
Wind Animal Petals: small, green, no scent : large, brightly coloured, scent and nectar
Pollen: Huge Amounts, small, light : Small amounts, large, sticky
Anthers: large, outside petals : small, inside petals
Stigmas: large and feathery, : smaller, rounded, inside petals
Outside petals
Example : grass, conifers : orchids, daisies, dandelions
What is fertilisation?
“Fertillization is the union of the male and female gametes”
Pollen grains lands on the stigma and forms pollen tube
Tube nucleus cause pollen tube to grow down through the style and into ovule
Tube nucleus dies
Double fertilization:
One of the male gamete nuclei joins with the egg nucleus to form diploid zygote
The second male gamete with the 2 polar nuclei to form a triploid endosperm
How does the seed form ?
After fertilisation the ovule becomes a seed
The triploid endosperm grows rapidly and absorbs nucellus
The zygote grows by mitosis to form the embryo
Embryo consists of a plumule and a radical
As the embryo grows it produces one or two seed leaves or cotlydons. The cotlydons are diploid and absorbs the endosperm to act as a food store in the seed
The walls of the ovule (integuments) become the seed coat(testa)
What are the types of seed?
Plants that form a seed with single seed leaf are monocots
Plants with 2 seed leaves are dicots
Presence/ absence of endosperm:
- in monocots the cotlydon absorbs food from endosperm and passes it on to embryo
- At maturity monocots seeds have some endosperm - “Endospermic”
- in ducts the cotlydons absorb food from the endosperm and act as stores
- dicot seeds do not have endosperm at maturity
What are fruits?
Seeds produce growth regulators such as auxins which stimulate the production of fruit
A fruit normally forms from the ovary
Fruits protect seeds and help disperse them
- some fruits are dry – grass and cereal grains
- many fruits are moist and edible -grapes and oranges
Seedless fruit
Formation of fruit without seed is called parthenocarpy
E.g.. bananas oranges
Seedless fruits are produce commercially in 2 ways
- Special breeding programmes - spraying plants with growth regulators such as axins stimulate them to make seedless fruit
What are fruits?
Seeds produce growth regulators such as auxins which stimulate the production of fruit
A fruit normally forms from the ovary
Fruits protect seeds and help disperse them
- some fruits are dry – grass and cereal grains
- many fruits are moist and edible -grapes and oranges
Seedless fruit
Formation of fruit without seed is called parthenocarpy
E.g.. bananas oranges
Seedless fruits are produce commercially in 2 ways
- Special breeding programmes - spraying plants with growth regulators such as axins stimulate them to make seedless fruit
What is dispersal ?
“Dispersal is the carrying of a seed as far possible from the parent plant”
Benefits:
- To reduce competition
- To increase chances of survival
- To find new areas for growth
- To increase numbers of the species
Methods:
Wind-
- some seeds are very small and blown long distances by wind
- dandelions have feathery parachute for larger seed
- anymore have winged seeds
Water
- Water lilys and coconuts have light air filled fruits that float on water
Animal dispersal
- sticky fruits attach to animal and fall off later e.g. buttercup
- edible fruits like blackberries are eaten, the seeds are not digested and pass out of the animal
Self- dispersal
- some plants explode e.g peas
To investigate the effects of water, oxygen and temperature on germination
Place filter paper in the base of four Petri dishes
Add water to filter paper in dishes A,C and D
Place 5 seeds in each Petri dish
Dish C is placed in refrigerator at 4 degrees, other dishes left at room temperature 20 degrees
Dish D place in a jar that contains anaerobic conditions. Anaerobic conditions created using an anaerobic kit that absorbs water
Dish A is control as it has all 3 factors
The dishes are left in place for a few days
Results show seeds need water, oxygen and suitable temperature