Describe the structure and functions of fruits and seeds.

State the meaning of the term ‘fertilisation’ - fusion of a male gamete from pollen with a female gamete in the ovule to produce the embryo.

FERTILISATION The fusion of a male gamete from pollen with a female gamete in the ovule to produce the embryo.

Fertilisation is the process where a male nucleus (gamete cell containing a single set of chromosomes “Haploid”) contained in a grain of pollen, joins with the female nucleus (gamete) contained in an ovule in the ovary. This union forms a cell containing the 2 sets of chromosomes (called a Zygote “Diploid” cell) which will result in a single seed. The pollen settles on the stigma. From the pollen grain a tube grows down the style, controlled by the tube cell nucleus, to the ovary entering via the micropile and into an ovule. Travelling behind the tube nuclei is a generative cell. Before entering the ovary this divides into 2 haploid sperm cells, each with a single set of chromosomes. On entering the ovary one cell fuses with the egg cell which forms the new diploid cell and the seed embryo. The second fuses with the polar nuclei and forms the seed food source (cotyledons) of the seed.

GAMETE

EMBRYO Radicle–embryonic root; Plumule – embryonic shoot; Hypocotyl – joins root to cotyledon; Epicotyl – joins shoot to cotyledon;

CHROMOSOME

HAPLOID

DIPLOID

ZYGOTE

POLLEN TUBE

MICROPYLE small hole, entry point for pollen tube into the ovule for fertilisation, now entry point for water and air into the seed for germination (can induce dormancy by being blocked with wax which can be removed by soaking seed in warm water prior to sowing);

POLAR NUCLCEI

TUBE NUCLEI

GENERATIVE CELL

State the meaning of the terms ‘fruit’ and ‘seed’ - a fruit is formed from the ovary after fertilisation. A seed is formed from the ovule after fertilisation.

FRUIT A fruit is formed from the ovary after fertilisation (an apple). function of: Fruit: Distribution and protection of the seed – may impose dormancy (hormonal):

SEED Seed is formed from the ovule after fertilisation (often enclosed within the fruit, e.g., apple pip). The EMBRYO of a new plant Natural regeneration of the plant, a means of distribution and protection of the embryo, may impose dormancy (hard seed coat: Lathyrus or immature embryo: Ginkgo), give rise to a new plant.

State the function of fruits and seeds - Fruit: distribution and protection of the seed and may impose dormancy. Seed: distribution and protection of the embryo, may impose dormancy, gives rise to new plants.

FRUIT A fruit is formed from the ovary after fertilisation (an apple). function of: Fruit: Distribution and protection of the seed – may impose dormancy (hormonal):

DEHISCENCE fruit splits open to release the seeds, e.g., Papaver orientalis;

INDEHISCENCE fruit does not split open, falls off and rots, e.g., nut Quercus robur;

SUCCULENT FRUIT fruit has a fleshy pericarp when ripe, e.g., drupe Prunus persica peach.

PERICARP

MESOCARP

ENDOCARP

EXOCARP

SILIQUE

FALSE FRUIT A false fruit is where the fruit forms from the receptacle not the ovary, e.g., Strawberry, or where you have an aggregate of several small fruits, e.g., Raspberry or where a fruit forms with no seeds inside, e.g., Cucumber, a parthenocarpic fruit

PARTHENOCARPIC

Describe the means by which seeds are dispersed - wind: (wing, parachute and censer (papaver)); water*; explosive; animals: (attachment, scatter hoarding and frugivory). TWO plant examples for EACH of the above except where indicated * where only ONE is required.

SEED DISPERSAL

WIND DISPERSAL (SEED) Winged seed (Samara): Acer Fraxinus, Ash Parachute: Taraxacum, Dandelion Asclepias curassavica, Milkweed

Seeds shaken from the fruit as the stem moves to and fro in the wind: Papaver

Meconopsis betonicifolia

WINGED SEED

SAMARA

WATER DISPERSAL (SEED) Iris pseudacorus, Yellow Flag Iris:

EXPLOSIVE DISPERSAL (SEED) Explosive:

Impatiens sultani

Geranium “Johnson’s Blue”

ANIMAL DISPERSAL (SEED) Attachment: Arctium lappa, Burdock

Bidens cernua, Nodding Bur Marigold

SCATTER HORDING Quercus robur, Oak Corylus avellana, Hazel nut

FRUGIVORY DISPERSAL (SEED) The fruit is ingested by the animal/moved/excreted and so dispersed away from the parent plant.

Waxwing eating Sorbus fruit:

Sorbus aucuparia Cotoneaster horizontalis Gravity: Apple.

Describe the internal and external structure of the seed and state the function of the various parts: testa, cotyledon, embryo, radicle, plumule, hypocotyl, epicotyl, endosperm, hilum, micropyle. Examples to be studied to include French bean (Phaseolus vulgaris) and broad bean (Vicia faba).

SEED STRUCTURE

MONOCOT SEED

DICOT SEED

TESTA protective seed coat (may induce dormancy – hard, waxy)

COTYLEDON Cotyledon: seed leaves, 2, food store for the embryo;

RADICLE First part to emerge from the seed, forming the main root. embryonic root

PLUMULE Plumule – embryonic shoot;

HYPOCOTYL Hypocotyl – joins root to cotyledon;

EPICOTYL Epicotyl – joins shoot to cotyledon;

ENDOSPERM Endosperm – food store in monocotyledon seed replacing cotyledon food store in dicotyledonous seed;

HILUM Hilum – attachment scar;

MICROPYLE small hole, entry point for pollen tube into the ovule for fertilisation, now entry point for water and air into the seed for germination (can induce dormancy by being blocked with wax which can be removed by soaking seed in warm water prior to sowing);

RADICLE First part to emerge from the seed, forming the main root. embryonic root

COLEOPTILE Coleoptile – protective sheath over the plumule;

COLEORHIZA Coleorhiza – protective sheath over the radical;

ALEURONE Aleurone – single layer of live cells, very chemically active in the seed and at germination

Describe ONE example of epigeal germination and ONE example of hypogeal germination, germination of French bean (Phaseolus vulgaris), and broad bean (Vicia faba).

GERMINATION

EPIGEAL GERMINATION Epigeal germination: the cotyledons in the seed are raised by the hypocotyl above the soil’s surface; eg. french bean phasoleus vulgaris

HYPOGEAL GERMINATION Hypogeal germination: the cotyledons in the seed remain below the soil surface and the plumule is raised above the soil surface by the epicotyl.