Sexual Reproduction in Plants

Name the parts of the stamen (male organ)

Anther and filament

Name the parts of the carpel (female organ)

Stigma, style, ovary and ovule

Name some features of insect-pollinated flowers

-Coloured, scented petals

-May produce nectar

-Anthers inside flower

-Stigma inside flower

-Stigma small and sticky

-Pollen sticky

-Few pollen grains

What is the difference between pin-eyed and thrum-eyed?

Pin-eyed has the stigma before the anthers, whereas thrum-eyed has the anthers before the stigma

Name some features of wind-pollinated flowers

-No petals

-No nectaries

-Anthers outside flower

-Stigma outside flower

-Stigma large and feathery

-Pollen light and dry

-More pollen grains

Describe the development of the male gamete

-Diploid pollen mother cells undergo meiosis

-Forms a tetrad (four haploid cells), which become four pollen grains

-Tapetum provides nutrients to developing pollen grains

-Haploid nucleus undergoes mitosis to produce two nuclei (generative and tube)

-Generative nucleus produces two male nuclei by mitosis

What is dessication?

When tension pulls the walls of the anther apart and the edges of the pollen sacs curl away so that pollen grains can be carried away by insects or the wind.

Describe the development of the female gamete

-In each ovule a megaspore undergoes meiosis, making four haploid cells (three disintegrate)

-Remaining cell undergoes three rounds of mitosis, producing eight haploid nuclei

-Two nuclei fuse to make a diploid nucleus called the polar nucleus

What are the names of all the cells in an ovule?

3 antipodals, one polar nucleus, 2 synergids and an egg cell (oosphere)

Define pollination

The transfer of pollen grains from the anther to the mature stigma of a plant of the same species

Define self-pollination

When the pollen from the anthers of a flower is transferred to the mature stigma of the same flower or another flower of the same plant

Define cross-pollination

When pollen is transferred from the anthers of one flower to the mature stigma of another flower on another plant of the same species

What are the consequences of self-pollination?

-Greater chance of producing harmful allele combinations

-Less genetic variation

What is an advantage of self-pollination?

It can preserve successful genomes that are suited to a relatively stable environment

What are the consequences of cross-pollination?

-Reduced chance of producing harmful allele combinations

-Allows species to survive in a changing environment (sharing of successful genomes)

-Generates more genetic variation

How is cross-pollination ensured in flowering plants?

-Anther below stigma so pollen cannot fall on it

-Separate male and female flowers on same plant

-Separate male and female plants

Define fertilisation

The process in which a male gamete fuses with a female gamete to produce a zygote

Describe the process of double fertilisation in flowering plants

-Pollen grain lands on stigma and produces a pollen tube

-Pollen tube grows down the style, through the gap in the integuments, the micropyle and passes into the embryo sac

-Pollen tube tip opens, releasing two male gametes into the embryo sac

-One male gamete fuses with egg cell to form a diploid zygote

-Other male gamete fuses with polar nucleus to form the endosperm nucleus, which divides by mitosis repeatedly to produce a tissue that provides nutrients to the developing embryo

Describe the process of fruit and seed development

-Zygote divides by mitosis, becoming an embryo consisting of a plumule and radicle

-Triploid endosperm develops into a food store

-Integuments dries out and becomes the testa

-Ovule becomes the seed

-Ovary becomes the fruit

Define dicotyledon

When a seed has two seed leaves or cotyledons

Define monocotyledon

When a seed has only one seed leaf or cotyledon

What seed developments have contributed to the success of angiosperms?

-Chemically resistant testa to survive adverse chemical conditions

-Low metabolic rate to survive cold weather

-Endosperm provides nutrients, which lasts until seedling can adequately photosynthesise

-Seed water content reduced to 10% to survive very dry conditions

Define germination

The biochemical and physiological processes through which a seed becomes a photosynthesising plant

What are the three main requirements for successful germination?

-Suitable temperature (5-30 degrees) for optimum enzyme activity

-Water to mobilise enzymes and vacuolate cells

-Oxygen for aerobic respiration

Describe the series of events that follow the secretion of gibberellic acid

-GA switches on genes that produce protease and amylase

-Proteases hydrolyse proteins to amino acids, which are used to make amylase

-Amylase hydrolyses starch in the endosperm

-Maltose and glucose produced diffuse into the embryo and are respired for energy