from zygotes to seeds and fruits ap biology spring 2011

From Zygotes to Seeds and Fruits

AP BiologySpring 2011

Making a lateral cut through an ovary of different flowering plants shows variation

Some are divided into more than one chamber, with more than one ovule attached to the ovary wall

Part of the wall may become a tissue mass in the center of the ovary

Figure on page 532

Variation in embryo sporophyte development

Ex. Shepherd’s purse- eudicot• Two cotyledons which develop from 2 lobes

of meristematic tissue • Embryos absorbs nutrients from endosperm

and stores them in cotyledons

•

Ex. Monocots:• Monocots have one cotyledon • Most monocot embryos do not tap into

nutritive tissue until after germination

Until embryo sporophyte fully formed, parent plants transfer nutrients to ovule’s tissue

Food accumulates in endosperm or in coyledons

Ovule will eventually pull away from ovary wall

Seed coat forms Embryo, food reserves, and coat =

seed• Seed = mature ovule

Only flowering plants make seeds in ovaries, and only they make fruits

Several ways to categorize fruit• Origin • Composition• Appearance

Simple fruits: one flower, originate in a single or fused carpel • Ex. Cherries, apples

Aggregate fruits: one flower, originate in several unfused carpels and become a cluster of several fruits• Ex. Strawberries, raspberries

Multiple fruits: start out as a cluster of individually pollinated flowers that grow together and fuse into a single body • Ex. Figs, pineapples

True fruit: only the ovarian wall and its contents

Accessory fruit: other floral parts, such as the receptacle, expand right along with the ovary • Ex. Watermelons, apples

Dry fruit: • Dehiscent: fruit wall splits along definite

seams to release the seeds inside Ex. Capsella pods and pea pods

• Indehiscent: wall does not split open, seeds are dispersed inside intact fruit wall Ex. Acorns, grains (corn), sunflowers, maples,

strawberries

Fleshy fruit:• Drupe: have a pit (stone hard jacket around

one seed; sometime more), and fleshy fruit that encloses the pit Ex. Cheeries, peaches, apricots, almonds, olives

Fleshy Fruit:• Berry: has one to many seeds, no pit, and

fleshy fruit• Ex. Grapes, tomatoes, lemons, oranges,

grapefruit• Pepo: hard rind on ovary wall (pumpkins,

watermelons, cucumbers)• Hesperidium: leathery rind on ovary wall

(citrus fruits)

Pome: has seeds in a somewhat elastic core tissue and fleshy accessory tissues that encloses its core • Ex. Apples, pears

To categorize an apple:• Simple fruit: originates from one flower• Accessory fruit: fleshy receptacle expands

around five carpels• Pome: carpels form an elastic core in fleshy

accessory tisue