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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