RHS Level 2 Certificate year 1 Week 30


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RHS Level 2 Certificate year 1 Week 30

  1. 1. RHS Level 2 Certificate Review of cells, pollination and fertilization and fruits
  2. 2. 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
  3. 3. 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
  4. 4. Cell diagram
  5. 5. Structure of a typical insect pollinated flower
  6. 6. Structure of a typical wind pollinated flower
  7. 7. 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)
  8. 8. Pollination • Agents have to be used to transfer pollen • Animals: insects, birds, bats mice etc…. • Wind • Water currents
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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 two identical haploid cells •pollen grain – two cells form a single pollen grain
  13. 13. • One female gametophyte can form in each ovule of a flower’s ovary. – 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
  14. 14. • 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
  15. 15. • Flowering plants go through the process of double fertilization. •female •gametophyte Pollen tube •egg •sperm •polar nuclei •ovule
  16. 16. • Flowering plants go through the process of double fertilization. •endosperm – one sperm fertilizes the egg and forms a •seed coat diploid zygote which has DNA from both parents – other sperm unites with polar nuclei, forming endosperm – endosperm provides •embryo food supply for embryo
  17. 17. • Each ovule becomes a seed. • The surrounding ovary grows into a fruit.
  18. 18. 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.
  19. 19. 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