Chapter 24.3

Seeds and Fruit

Why?

The seeds and fruits formed help ensure survival of the next generation

Seed formation

After fertilization Zygote divides = embryo Triploid cell divides = endosperm Ovule wall = seed coat

Fruit formation

Fruit – the structure that contains the seeds of an anthophyte

Fruit – the enlarged ovary surrounding the seed

Can be made up of other organs as well.

Fruits

Fleshy fruits – apples, grapes, melons, tomatoes, cucumbers

Dry fruits – peanuts, sunflower seeds, walnuts. The ovary around the seeds hardens

Seed dispersal

Fruits aid in dispersal Dispersal reduces competition Animals – digestion and/or carrying

the seed on the body Wind – dandelion, tumbleweed Water – coconut and water lilies

Pictures – from flower to fruit

http://www.cas.vanderbilt.edu/bioimages/pages/fruit-devel.htm

What about seedless fruit?

Ex. Watermelon and bananas Triploid plants – prevents meiosis

from happening and no gametes are produced

So where do the plants come from if there are no viable seeds?

Bananas – vegetative reproduction Watermelons – Cross a diploid with a tetraploid

to produce a triploid seed Diploid (2) + Tetraploid (4) = 6 sets of

chromosomes Divide 6 by meiosis to get 3 sets of

chromosomes. Pollination triggers fruit formation – without

seeds. The plants must be grown with a diploid variety

for pollen

Seed germination

Dormancy – the period of inactivity in a mature seed

Varies greatly between species Ends when the seed germinates Germination – the beginning of the

development of the embryo into a new plant

Germination

Water – activates the metabolism Some seeds have specific

requirementsEx. Animals digestive system,

freezing temps, extensive soaking in saltwater, specific daylengths, exposure to fire.

Dicot germination

Radicle – embryonic root appears first

Hypocotyl – portion of stem nearest seed

Cotyledon – plants first leaves In monocots the cotyledon remains

below the surface

Vegetative reproduction

A new plant is produced from a stem, root or leaf

This is essentially cloning – producing new plants that are genetically identical to their parents

Tissue culture and/or cuttings.