rhs level 2 certificate year 1 week 30
TRANSCRIPT
RHS Level 2 Certificate
Review of cells, pollination and fertilization and fruits
Learning outcomes
• Identify and describe the different parts of the plant cell
• Describe the processes of wind and insect pollination
• Define pollination • Define fertilization• Describe the process of fertilization• Classify various types of fruit
Plant Cells
• Cell Wall – made of cellulose, holes allow plasmodesmata (cytoplasm) out to connect the cells to each other chemically
• Cell membrane – surrounds the living content of the cell; inside the cell wall.
• Cytoplasm – the living content of the cell• Nucleus – contains chromosomes that are strands of DNA• Vacuole – sac containing dilute sugars and nutrients and
waste products.• Chloroplast – contains chlorophyll, site of photosynthesis• Mitochondria – site of respiration, releases energy from
carbohydrate
Cell diagram
Structure of a typical insect pollinated flower
Structure of a typical wind pollinated flower
Pollination
• The transfer of pollen from the anther (where it is made) to the stigma.
• Cross pollination: pollen transferred to a different individual of same species
• Self pollination: pollen transferred to the stigmas of the same flower (hermaphrodite flower) or to a female flower on the same plant (monoecious)
Pollination
• Agents have to be used to transfer pollen
• Animals: insects, birds, bats mice etc….
• Wind• Water currents
Wind Pollination
• Flowers have no need to attract insect
• Stigma and stamen usually small and on long stalks to catch the wind
• Huge quantities of tiny light coloured pollen grains produced
Wind Pollination
• They are the usual cause of hay fever!
• Wind pollen is usually small and light
• Often contains air sacs• Grasses and many
trees are wind pollinated
Insect Pollination
• Insect pollen is often sticky!• Nectar rewards the insect• Pollen often contains
carbohydrates as food for the insect
• Flowers have ultra-violet sensitive pigments that direct the insects to the stamen and pistil
Fertilization takes place within the flower.
• Male gametophytes, or pollen grains, are produced in the anthers. – Haploid male gametes
produced in anthers
by meiosis– each gamete divides by
mitosis to form twoidentical haploid cells
– two cells form asingle pollen grain
•pollen grain
– Haploid female gametes produced in ovule by meiosis – one gamete develops into female gametophyte – female gametophyte contains a number of cells – one cell has two nuclei, or polar nuclei (one set of chromosomes
each – a double haploid)– one haploid cell will develop into an egg
• One female gametophyte can form in each ovule of a flower’s ovary.
• Pollination occurs when a pollen grain lands on a stigma.
– The pollen must be compatible to fertilize the ovum – that means that the pollen must ‘recognise’ the chemical signature of the stigma
– If the pollen is compatible it is stimulated to divide by the chemicals produced by the stigma. If not compatible it will die.
– one cell from pollen grain forms pollen tube– other cell forms two sperm that travel down tube
• Flowering plants go through the process of double fertilization.
•female•gametophyte
•ovule
•egg
•sperm
•polar nuclei
Pollen tube
•endosperm
•seed coat
•embryo
– one sperm fertilizes the egg and forms a diploid zygote which has DNA from both parents
– other sperm unites with polar nuclei, forming endosperm
– endosperm provides food supply for embryo
• Flowering plants go through the process of double fertilization.
• Each ovule becomes a seed.• The surrounding ovary grows into a fruit.
Fruits
• The part of the reproductive structure surrounding the seeds, e.g. pods and nuts as well as the fruits that we eat.
• Develops from the ovary; if the structure around the seeds develops from other parts of the flower it is a ‘false fruit’
• Parthenocarpy is the formation of fruit without fertilization
• Classification of fruit – a number of systems and no botanical agreement.
Classification of Fruit – simple scheme
• Simple fruit – formed from one ovary, may contain one or many seeds. E.g. Prunus x domestica
• Aggregate fruit – formed from the fusion of many ovaries in one flower. E.g. Raspberry Rubus ideaus
• Compound fruit – Formed from the ovaries of several grouped flowers e.g. Pineapple Ananus comosus
• Dehiscent – splits open to release seeds e.g. Lathyrus odoratus pod
• Indehiescent – does not split open e.g. Quercus robur acorn• Berry – a simple fruit with no hard layer of endocarp around
the seeds e.g. Lycopersicon esculentum• Drupe – a simple fruit with a stony layer of endocarp around
the seed e.g. Prunus x domestica