Sexual Reproduction in Plants

• Flowers are the reproductive organ of the plant

  • contain both male and female reproductive parts
• Plants produce pollen - contains a nucleus inside that is the male gamete

  • unlike the male gamete in humans (sperm), pollen is not capable of locomotion
  • locomotion - moving from one place to another
• Plants have to have mechanisms in place to transfer pollen from the anther to the stigma aka pollination

  • the stigma receives the pollen
• • Pollination - the transfer of pollen grains from the anther to the stigma
• Cross pollination - pollination of a flower from a different flower or plant of the same species

  • improves gentic variation
  • relies on the presence of pollinators - a problem if those pollinators are missing but this doesn’t apply to wind-pollinated plants
• Self pollination - pollination of a flower by pollen from the same flower or another flower on the same plant
• Self pollination is the last resort

  • little genetic variation as the gametes come from the same parents
  • little variation means its difficult for them to adapt to new environments - low survival chances
• 2 ways to avoid self pollination

  • have stigmas and anther ripen at different times
  • separate the male and female parts
• 2 main pollination methods:

  • transferred by insects (or other animals like birds)
  • transferred by wind
• Structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function
• Parts of the flower:

  • stem - links the flower to the rest of the plant
  • receptacle - links the flower to the top of the stem
• Parts of the flower diagram

  A) protects unopened flower

  B) brightly coloured in insect-pollinated flowers

  C) produces and releases the male sex cell

  D) top of the female part of the flower which collects

  E) female sex cell (ovum)

  F) contains

  G) female sex cell found inside the ovary

  H) produces

  
• Flower structure diagram

  A) petal

  B) stamen

  C) anther

  D) filament

  E) sepal

  F) stem

  G) receptacle

  H) carpel

  I) stigma

  J) style

  K) ovary

  
• Insect-pollinated flower structure:

  A) ovary

  B) ovule

  C) nectary

  D) large and brightly coloured

  E) attract insects

  F) present

  G) entices insects

  H) push past stamen to get nectar

  I) small

  J) transfer

  K) efficiently

  L) high chance of successful

  M) larger, stick and spiky

  N) attach

  O) inside

  P) stiff

  Q) firm

  R) inside

  S) sticky

  
• Wind-pollinated flower structure

  A) stamen

  B) filament

  C) stigma

  D) small and dull

  E) green or brown

  F) absent

  G) waste energy

  H) attract insects

  I) large amounts

  J) transferred

  K) better

  L) chance

  M) successful

  N) smooth, small and light

  O) easily blown

  P) outside

  Q) swinging loose

  R) easily

  S) outside

  T) feathery

  
• Pollen produced by insect and wind-pollinated flowers is different:

  • Insect pollinated flowers - produce smaller amounts of larger, heavier pollen grains that often contain spikes or hooks on the outside so they are better able to stick to insects
  • Wind pollinated flowers - produce large amounts of small, lightweight pollen grains that are usually smooth
• Fertilisation - when a pollen nucleus fuses with an ovum nucleus in the ovule

  • only happens if the pollen lands on the right type of stigma e.g. the same species
• Pollen cannot move to the ovary of a plant so needs the pollen tube to reach the female nucleus in the ovary

  • nucleus in the pollen grain slips down the tube and grows down the style towards the ovary
• Pollen moving down diagram

  A) pollen

  B) pollen tube

  C) ovary

  
• Ovary contains one or more ovules which each contain an ovum with a female nucleus that a a male pollen nucleus can fuse with

  • when the nucleus’ fuse, the ovule is fertilised and a zygote is created
• Pollen fusion diagram

  A) pollen grain nucleus

  B) female nucleus

  
• Zygotes will divide and form a seed within the ovule

  • different plants have different numbers of ovules which is why different fruits (develops from ovary) have different amounts of seeds (develops from ovules)
• Pollination vs fertilisation

  • Pollination is the plant’s equivalent to human sexual intercourse
  • Fertilisation happens in both humans and plants as its the fusion of a male sex cell with a female sex cells
• Pollination Diagram 1:

  A) (containing male nucleus) lands on stigma

  B) pollen tube

  C) grow

  D) style

  E) stigma

  F) style

  G) ovary

  H) ovule

  I) ovum

  J) micropyle

  K) opening

  L) ovule

  M) nucleus

  N) pollen tube

  O) female nucleus within ovum

  P) pollen tube

  Q) ovule

  R) micropyle

  
• Pollination Diagram 2:

  A) nucleus

  B) fuses

  C) ovum nucleus

  D) fertilisation

  E) ovary wall

  F) fruit

  G) ovule

  H) seed

  
• Ovule and ovum difference

  • For plant reproductions, the ovule contains the ovum aka female sex cell inside it
• Nuclei vs nucleus

  • nuclei - plural for nucleus
  • nucleus - single nucleus
• Germination - the start of growth in the seed

  • everything needed to start life is within the seed
  • certain conditions are needed before germination
• 3 factors required for successful germination

  • water - allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur
  • oxygen - used for respiration so energy can be released for germination
  • warmth - germination improves as temperature rises because the reactions which take place are controlled by enzymes
• Carbon dioxide and light makes no difference in germination
• Rules for biological drawings:

  • occupy at least half of the space provided
  • use single unbroken lines for structures and out lines
  • no shading
  • always use sharp pencil
  • use a ruler to draw a straight line for labels
  • don’t use arrow heads for labelling and make sure the lines touch the structures
• Where is the receptacle?

  On the top part of the stem
• What are 3 features of wind-pollinated pollen?

  Smooth, lightweight, large amount
• 3 features of insect-pollinated pollen

  sticky, heavy, small amount
• What are two ways plants prevent self pollination?

  They have the stigmas and anther ripen at different times or have the female and male parts separate
• Explain the process of fertilisation in plants

  Pollen lands on the stigma on the plant which stimulates a pollen tube to be grown in the style to the oval. The nucleus of the pollen travels down that tube and enters the ovule, fertilising the ovum. This then causes the ovule to swell and ripen into a seed and the ovary wall becomes a fruit.
• Define Germination

  The start of growth in the seed
• What are the 3 factors needed for germination and why?

  Water is needed as it softens the seed coat and allows the enzymes in the embryo to work so that the embryo can swell and divide. Oxygen is needed as it allows respiration to happen so energy can be put into germination. Warmth is needed as it speeds up the enzymes, speeding up the processes carried out in germination.
• What are the rules for biological drawings?


  occupy at least half of the space provided

  use single unbroken lines for structures and out lines

  no shading

  always use sharp pencil

  use a ruler to draw a straight line for labels

  don’t use arrow heads for labelling and make sure the lines touch the structures
• Organisms need energy for 4 processes:

  • growth
  • movement
  • reproduction
  • repair and maintenance