CHAPTER 10 – PLANT

REPRODUCTION, GROWTH AND

DEVELOPMENT10.1 Sexual Reproduction in

Flowering Plants

FLOWER STRUCTUREReview from 29.4!

Sepals: surround unopened flower bud; whorl around petals when open

Petals: size, shape, colour, odor used to attract pollinators

Stamen: composed of anther (sac-like container) and filament (slender stalk)

Male reproductive parts

Pistil: female reproductive parts; vase-like shape

Stigma (enlarged, sticky knob), Style (slender stalk), and Ovary (enlarged base, contains ovules)

Perfect Flower (Bisexual): has all parts (sepals, petals, stamens, and a pistil)

Imperfect Flower (Unisexual): missing some parts

Staminate Flowers: only have stamens Pistillate Flowers: only have pistils

Monoceious: staminate and pistillate flower on one plant

Diocecious: staminate and pistillate flower on separate plants

ALTERATION OF GENERATIONSInvolves 2 generations: sporophytes

and gametophytes

Diploid sporophytes produce haploid spores through meiosis

I. GAMETOPHYTE DEVELOPMENT

Heterosporous – ovules (pistil) produce megaspores; anthers (stamen) produce microspores

Microspores pollen grains (sperm-containing microgametophyte or male gametophyte)

Megaspores egg-containing embryo sac (megagametophyte or female gametophyte)

Fertilization Zygote Embryo within seed Germination Growth of new

sporophyte plant!

In ovules...

megaspore undergoes meiosis produces 4 haploid megaspores

3 megaspores disappear, remaining 1 undergoes mitosis

Results in megagametophyte (embryo sac)

cytoplasm differentiates and produces polar nuclei (2 nuclei in centre, 3 at each opposite end)

In anthers...

Pollen sacs contain microspores undergoes meiosis and produces 4 haploid microspores

microspores separate, each one produces a pollen grainNucleus undergoes mitosis, creating

2 nuclei called tube cell and generative cell

II. POLLINATION

When pollen is windblown or carried to the stigma of the same type of plant

Pollen grain germinates and develops a long pollen tube Grows within style, reaching ovule

in ovary mitosis of generative cell produces 2

sperm (no flagella)

Double fertilization occurs...One fertilizes egg, forming a zygoteOther fertilizes polar nuclei, forming endosperm nucleus

Endosperm nucleus divides, forming endosperm (food for developing plant)

zygote develops into multicellular embryo

Ovule wall hardens, forming seed coat

Seed consists of sporophyte embryo, stored food, and seed coat.

Ovary (and sometimes other floral parts) develops into fruit

GROWTH AND DEVELOPMENT

Involves cell division, cellular elongation, and cell differentiation into tissues then organs.

Development: set series of stages from a simpler to more complex form

Cellular Differentiation: specialization of structure and function

I. DEVELOPMENT OF DICOT EMBRYO single-celled zygote under endosperm

nucleus

endosperm nucleus divide by mitosis, producing mass of endosperm tissue

zygote divides upper part = embryo, lower part = suspensor (anchors embryo and transfers nutrient)

Cotyledons (seed leaves) develop embryo goes from heart-shaped to torpedo

shaped Shoot apex: shoot apical meristem = above ground

growth Root apex: root apical meristem = underground

growth

Endosperm is taken up by 2 cotyledons Epicotyl is above cotyledon, contributes to shoot

development Hypocotyl is below cotyledon, contributes to

stem development Radiclecontributes to root devleopment

Result: Embryo + stored food now contained in seed

DIFFERENCE BETWEEN MONOCOTS AND DICOTS

monocots = 1 cotyledon

monocot cotyledon rarely stores food absorbs food from endosperm and

passes it to embryo

dicot cotyledon usually stores food

II. DEVELOPMENT OF SEEDS AND FRUITS

Fruit: a mature ovary that usually contains seeds

Ovary wall thickens to become pericarp (fleshy) apple, tomatoes, peaches

dry fruits have dry pericarps legumes (peas and beans) split

along 2 sides or seams

Aggregate fruits develop from individual ovaries (blackberries, strawberries)

III. SEED DISPERSAL

adaptations to be carried by animals clover has hooks to attach to fur

eaten by animals, then deposited in stool

buried by animals

ocean currents – ex. carry coconuts

wind – wooly hairs, plumes and wings

IV. SEED GERMINATION

Germination: when an embryo grows into a seedling

Dormancy: time during which no growth occurs, even when conditions are favourable

Growth affected by presence of water and oxygen, temperature, dormancy period, etc.

Growth requires regulation (inhibitors and stimulators)

fleshy fruits – inhibitors that prevent growth until seeds are removed/washed

stimulators may include mechanical actions (ex. fire making seed coat permeable to water)

Water uptake causes seed coat to burst!

V. DICOT VS. MONOCOT DEVELOPMENTDicot 2 cotyledons (seed leaves) shrivel up

Plumule: epicotyl bears young leaves

Dicot seedling breaks through ground... Shoot is hook shaped hypocotyl becomes part of stem radicle develops into roots

Can also grow in the dark Etiolation: stem elongates,

roots/leaves are small, plant lacks colour

resumes normal growth when light becomes normal

Monocot endosperm is food storage tissue

(cotyledon has no storage role) plumule and radicle covered in

protective sheaths (coleoptile and coleorhiza)

burst through coverings when germination occurs