Reproduction

• The male reproductive system consists of the testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, penis, scrotum, and accessory ducts.
• Reproduction


  The perpetual continuation of life for the survival of a species (i.e organism which share similar characteristics & can interbreed to produce fertile offspring)
• Types of reproduction


  • Asexual Reproduction
  • Sexual reproduction
• Asexual Reproduction


  Reproduction in which new organisms are formed from a single parent without a gamete reproduction. This is reproduction without fertilization i.e. no fusion of gametes.
• Asexual Reproduction


  • The offspring are genetically identical to each other & to the parent organism and are referred to as CLONES
• Asexual Reproduction in Plants and Animals

  • Vegetative propagation
  • Budding
  • Cutting
  • Grafting
  • Layering
  • Fragmentation / Regeneration
• Budding


  A form of asexual reproduction in which a new organism is produced as an outgrowth. The outgrowth is later released as a self-supporting, identical copy of the parent.
• Cutting


  The cutting of about 20cm is trimmed at the base just below a joint & inserted firmly in good moist soil or water. Most plant e.g. roses are propagated through cuttings.
• Grafting


  A bud / shoot from the plant is inserted under the bark on the stem of another closely related variety. The bud then grows using water & nutrients supplied by the other plant , mostly suitable for propagation of apple trees, pear trees, rubber trees etc
• Layering


  A young branch that is still attached to a plant is bent downwards to the ground and held firmly to the ground using pegs (hooks) until it forms roots. (sometimes rooting powder can be applied to accelerate root development). Once the branch has fully grown into a plant, it is cut off from the parent plant so that it becomes independent.
• Fragmentation / Regeneration


  The breaking of an organism into two or more parts, each of which grow to form a new a individual. This form of asexual reproduction is common among less differentiated animals.
• Commercial Application of Asexual Reproduction in Flowering Plants
• Advantages of Asexual Reproduction

  • It is the simplest & shortest way of reproduction
  • The chances of offspring survival are greatly enhanced
  • There is no danger of gametes getting destroyed before fusion
  • Ideal for presentation of good characteristics within the population
  • Possible to produce a large number of offspring within a short time
• Disadvantages of Asexual reproduction


  • Defects from parents are easily passed to offspring
  • Inhibits evolutionary change
• Sexual Reproduction in Plants

  The transfer of pollen grains from the anther to the stigma
• Functions of parts of a flower

  • Stigma – receives pollen grains
  • Style – allows the pollen tube to pass through to the ovary
  • Ovary – produces female sex cells called ovules
  • Anther – produces the male sex cells called pollen grain
  • Filament – holds the anther
  • Petals – encloses parts of the flower ( protection)
  • Sepals – protects the ovary (and the general flower during the bud stage)
  • Flower stalk – holds the flower in position (attaches the flower to the plant)
  • Receptacle – where all the other parts of a flower are attached
• Pollination


  The transfer of pollen grains from the anther to stigma
• Types of Pollination


  • Self Pollination – the transfer of pollen grains from the anther to the stigma in the same flower, or the transfer of pollen grains from the anther to stigma of another flower on the same plant.
  • Cross Pollination – The transfer of pollen grains from the anther to the stigma of another flower of the same species.
• Agents of Pollination


  • Insects
  • Wind
• Characteristics of Wind Pollinated Flowers

  • Have dull petals
  • Small or no petals
  • Have feathery stigma
  • Light pollen grains produced
  • Lots of pollen grains produced
  • Have no scent
  • No nectar
• Characteristics of Insect Pollinated Flowers

  • Bright coloured petals
  • Have large petals
  • Plain stigma
  • Sticky pollen grains
  • Few pollen grains
  • Scented petals
  • Have nectar
• Fertilization


  The fusion of the male nucleus (from pollen grains) with female nucleus (from the ovules)
• Growth of the Pollen Tube

  1. Pollen grains land on stigma

  2. Pollen tube grows down style

  3. Pollen tube reaches ovary

  4. Pollen tube enters ovule

  5. Male nucleus fuses with female nucleus
• Embryo


  Develops from the fertilized egg (ovule). It has a plumule (which develops into shoot) and a radicle (which develops into roots). The embryo is attached to the cotyledons in – one in monocots & two in dicots. The embryo is found enclosed in seeds.
• Non-Endospermic Seed (Dicot) e.g. bean seed


  Testa {seed coat} – this is the tough outer cover in seeds. It protects the embryo from physical damage.<|>Cotyledon - this is where food is stored fro the embryo. Non Endospermic seeds (dicots) have two cotyledons. Endospermic seeds have one cotyledon<|>Micropyle – it is an opening left by the pollen tube on the testa. It allows water & O2 needed for germination to enter the seed to go<|>Embryo is made of the plumule – which develops into the shoot during germination, and the radicle – which grows in the root system.
• Environmental Conditions For Germination

  • Water
  • Oxygen
  • Suitable Temperature
• Water


  Adequate water is needed for germination to start & continue. Excess water prevents germination by probably excluding oxygen. The forces exerted by the accumulation of water into the seed may eventually rapture the testa. Water is also required to activate the biochemical reactions associated with germination because these take place in solution.
• Oxygen


  It is required for aerobic respiration. The energy released is used to run chemical reactions within the cells of the embryo during its period of growth.
• Suitable Temperature


  This will make enzymes to be activated thus chemical reactions will occur at the highest rate to make new cells. Each species of seeds have an optimum temperature for germination; (5 0C– 40 0C) is the temperature range suitable for seed germination.
• Role of Enzymes in Seed germination

  In the early stages of germination, the food reserves in the cotyledons mostly starch & proteins are acted upon by enzymes and converted to soluble products which pass to, & are used by the actively growing regions where protoplasms are being made. Glucose is formed from the stored starch & being used in various ways; e.g. In the synthesis of cellulose & incorporated into cell walls and in the process of respiration to generate energy needed in the growing regions.
• Seed Dispersal


  The transfer {scattering away} of seeds from the parent plant to new sites. After seed development either the entire fruit or the seed(s) contained within are dispersed from the parent plant.
• Advantages of Seed dispersal

  • It reduces chances of competition for nutrients & space
  • There is also more chance of finding a fresh area to colonize, thus increasing the overall species population in time. (it promotes plants diversity in different localities)
• Disadvantages of Seed dispersal

  • There is a possibility of not finding a suitable place for germination
• Mechanisms of Seed Dispersal

  • Animal
  • Wind
  • Water
  • Self dispersal mechanism (explosive release of seeds from the fruit)
• Animal Dispersed Seeds


  • They have hooks or spines with which they attach themselves to the skin, fur or wool of passing animals and thus carried over some distance before dropping off or being scratched off. E.g. goose grass, buttercup etc.
  • Contained in succulent fruits which have edible fleshly parts. E.g. tomatoes, strawberry, mulberry, wild berries, grapes etc. The fruit is eaten & digested but the seeds are resistant to digestive enzymes & pass unharmed through the gut of the animal to be deposited with faeces often on fertile soils.
• Wind Dispersed Seeds


  • Parachute fruits & seed – seeds of willow herb & the fruit of dandelion have projecting feathery hairs (parachute-like strutures) which increase their surface area. As a result, the seeds floats over long distances before sinking to the ground. It is therefore likely to be carried a long way from the parent plant by slight air current.
  • Winged fruits – Fruits of sycamore & ash trees have wing-like outgrowths from the ovary walls or leaf-like structures on the flower stalk. These wings cause the fruit to spin as it falls from the tree & slow down its fall. This delay increases the chances of the fruit being carried away in air currents.
  • Pepper pot effect – e.g. poppy has along flower on which hangs a dry hollow capsule (formed from the ovary) with one / more openings. The wind shakes the flower stalk and seeds are scattered on all sides through the openings in the capsule
• Water Dispersed Seeds


  • Some plants e.g. Coconut have a fibrous ovary wall which enables the fruit to float on water so that the seed is water dispersed.
• Self Dispersed Seed


  • Explosive fruits – the pods of flowers in the pea family dry up in the sun and shrivel. The tough fibres in the fruit wall shrinks & set up a tension forcing the fruit to split in half down the lines of weakness, the two halves curl back suddenly & flick out the seed.