1.1 Reproduction in Plants

• how can cross-pollination be ensured?

  - separate male and female flowers

  - separate male and female plants

  - the stamen and the stigma ripen at different times

  - the anther is lower than the stigma so pollen cannot fall onto the stigma (structural incompatibility)

  - the pollen from a plant cannot germinate on the same plant (genetic incompatibility)
• state the three genetic consequences of cross-pollination.


  - displays greater genetic variation as it combines gametes from two individuals in addition to independent assortment and crossing over during meiosis.

  - it reduces the chance of producing harmful allele combinations.

  - new combinations of genes means species can survive in a changing environment.
• state the three genetic consequences of self-pollination.

  - Displays less genetic variation than cross-fertilised species as self-fertilised only depend on independent assortment and crossing over during meiosis.

  - there is a greater chance of two potentially harmful recessive allele being brought together at fertilisation.

  - an advantage is that it preserves the successful combination of genes that are suited to a relatively stable environment.
• what does self-fertilisation result in?

  interbreeding.
• what is cross-pollination?


  the transfer of pollen from the anther to the stigma of a different plant.
• what is self-pollination?

  the transfer of pollen from the anther to the stigma of the same plant.
• what is the role of endosperm tissue?

  it provides nutrients for the developing embryo.
• describe the double fertilisation of an angiosperm.

  - one male gamete will fuse with the oosphere to form a diploid zygote (2n). This embryo develops into a new plant.

  - the other male gamete will fuse with the diploid polar nucleus to form a triploid nucleus, called an endosperm nucleus.

  - the endosperm will divide by mitosis to form endosperm tissue.
• describe the development of the pollen tube to allow male gametes to reach the ovule.

  - a compatible pollen grain lands on the stigma of a plant.

  - the tube nucleus codes for enzymes which hydrolyse the cells in the style and direct pollen tube growth.

  - the pollen tube grows downwards through the style and towards the ovule.

  - the pollen tube grows through the micropyle and into the embryo sac.

  - the pollen tube nucleus can now disintegrate.

  - the two male nuclei will now pass through the pollen tube and into the embryo sac.
• what is the function of antipodals?

  they have no function and degenerate.
• what is the function of synergids?

  they release chemicals, chemoattractants which direct the pollen tube.
• describe the development of a female gamete.

  - the megaspore mother cell undergoes meiosis to form four haploid cells.

  - three haploid cells disintegrate and the remaining cell enlarges and becomes the embryo sac

  - the remaining haploid cell undergoes three mitotic divisions to produce an embryo sac containing 8 haploid nuclei.

  - one of these nuclei becomes the egg cell.

  - the two polar nuclei present in the embryo sac fuse together to form a diploid polar nucleus.
• what is a nucellus in a female gamete?

  a layer of cells inside the integument, which is tough and protective.
• describe the process of dehiscence.

  the anther dries out which creates tension in the lateral groove causing the pollen sac to split and release pollen grains.
• describe the development of male gametes in plants

  the diploid pollen mother cell divides by meiosis into a tetrad of haploid immature pollen cells. The haploid nucleus divides by mitosis into a mature pollen grain, containing a haploid generative nucleus and tube nucleus. the process of dehiscence occurs so the haploid generative nucleus divides by mitosis into 2 male nuclei.
• what cells do pollen sacs contain?

  microspore mother cells (pollen mother cells)
• what is the function of the tapetum in the anther?

  It provides nourishment and protects the developing pollen cells from drying out.
• what are the parts of the cross section of an anther?

  epidermis, vascular strand, tapetum, parenchyma, pollen sac, lateral groove, fibrous layer, lateral groove.
• when do plants develop gametes to produce pollen grains and ovules, and why?


  during spring as weather conditions are more stable.
• what are the features of insect-pollinated flowers?

  - they have colourful petals sometimes with nectar guides.

  - they are scented and contain nectar (mostly composed of sucrose)

  - the anthers are within the flower

  - the stigma is within the flower

  - small quantities of sticky, sculptured pollen

  - large pollen grains produced
• why are wind-pollinated stigmas adapted to be feathery and stick outside of the flower?

  To increase the surface area and to increase the chance of pollen sticking to it.
• what are the features of wind-pollinated flowers?

  - Usually no petals, if so they are green and small

  - no scent/nectar

  - large feathery stigma hangs outside of the flower

  - anthers hangs outside of the flower

  - large quantities of smooth pollen

  - produces small pollen grains
• what is the main benefit of cross-pollination in flowers?

  It increases genetic variation.
• how are wind-pollinated flowers adapted to reduce the chance of self-fertilisation?

  The mature carpel (style/stigma/ovary) is above the mature stamen (anther/filament).
• what is a group of wind-pollinated flowers called?

  inflorescence.
• what two ways are plants pollinated?


  By wind or by insects.
• what is the difference between self-pollination and cross-pollination?

  Self-pollination is the transfer of pollen from the anther to the stigma in the same plant.

  Cross-pollination is the transfer of pollen from the anther to the stigma in a different plant.
• what is pollination?

  The transfer of pollen from the anther to the stigma.
• what is the female gamete in a flowering plant?

  ovum/ oosphere
• what is the male gamete in a flowering plant?

  Pollen
• what is the function of the receptacle?


  the stem where the flower organs are attached to
• what is the function of the ovules?

  they contain egg cells
• what is the function of the ovary?


  It contains ovules
• what is the function of the style?

  It keeps the stigma high above the anther in order to reduce the chance of self-fertilisation
• what is the function of the stigma?

  it is sticky, enabling pollen to stick to it
• what is the function of the filament?

  It supports the anther.
• what is the function of the anther?

  It contains four pollen sacs which split in the process of dehiscence and release pollen.
• what is the function of the nectary?

  It secretes nectar which attracts insects.
• what is the function of the corolla (more than one petal)?

  They attract insects, ranging from green to bright colours.
• what if the function of the calyx (lots of sepals)?

  It protects the flower before it blooms when it is a bud.