Sheryl Searcy Ninth Grade Center 2012 CONES & FLOWERS Reproduction in Seed Plants Chapter 24.

Sheryl Searcy Ninth Grade Center 2012

CONES & FLOWERS

Reproduction in Seed Plants

Chapter 24


REPRODUCTION WITH CONES & FLOWERS

Section 24-1


Life Cycle of Gymnosperms Reproduction of gymnosperms takes

place in cones which are produced by a mature sporophyte plant.– Pollen cones– Seed cones


Life Cycle of Gymnosperms


Structure of Flowers Flowers are reproductive organs that are

composed of four kinds of specialized leaves:– Sepals: outermost part, green, resembles leaves.– Petals: brightly colored, attract insects and other

pollinators.– Stamens: male gametophyte; the anther and a

filament inside the ring of the petals.– Carpel (pistils): female gametophyte; consists of

ovary, ovule, style, and stigma.


Structure of Flowers

Carpel


Flowers vary enormously in structure. Some flowerlike structures are actually

clusters of many individual flowers.

Structure of Flowers

Day Lilly Wisteria


Cycle of Angiosperms


SEED DEVELOPMENT & GERMINATION

Section 24-2


Seed Development As angiosperm seeds mature, the ovary

walls thicken to form a fruit that enclosed the developing seeds.


Seed Dispersal Dispersal by animals

– Seeds dispersed by animals are typically contained in fleshy, nutritious fruits.

Dispersal by wind and water– Seeds dispersed by wind or water are

typically lightweight, allowing them to be carried in the air or float on the surface of the water.


Seed Dormancy Contributing environmental factors

– Temperature– Moisture

Seed dormancy…– Can allow for long-distance dispersal (weeks or

months).– Can allow seeds to germinate under ideal

conditions.– Can allow seeds to reclaim a forest after a fire

(pine trees).


Seed Germination The early growth phase of plant embryo.


GROWTH RESPONSE IN PLANTS


Tropism A directional growth movement

made by a part of a stationary plant response to unilateral stimulus.


Graviotropism/Geotropism Importance:

– Provide firm anchorage for roots.– Ensure the plant gets adequate water & mineral salts

The root tip produces hormones which diffuse to the elongation region.– The hormones diffuse to the lower side due to gravity.– High hormone concentration inhibits growth in root.– The lower side grows slower than the upper side.– The root bends downward.


Phototropism Importance:

– Enables leaves to be in a position to receive as much sunlight as possible for photosynthesis.

The shoot tip produces hormones which diffuse downward:– The hormones diffuse to the shaded side due to the

presence of one-sided light.– High hormone levels stimulate growth in shoot.– The shaded side grows faster

than the lighted side.– The shoot bends towards the

light .


Thigmotropism The directional response of a plant organ to

touch or physical contact with a solid object.– This directional response is generally caused by the

induction of some pattern of differential growth.– This phenomenon is clearly illustrated by the

climbing tendrils of some plants, such as the sweet pea.

The tendrils actually "feel" the solid object, which results in

the coiling/closing response.


Hydrotropism Importance

– Ensures that a plant gets enough water as a raw material for photosynthesis & enough mineral salts to maintain normal growth.


Photoperiodism Physiological reaction of organisms to the

length of day or night. Occurs in plants and animals. The developmental responses of plants to

the relative lengths of the light and dark periods.– Many flowering plants use a photoreceptor protein,

such as phytochrome or cryptochrome, to sense seasonal changes in night length, or photoperiod, which they take as signals to flower.


Plant Hormones Chemicals that regulate plant growth. Auxins: most common plant hormone

– Regulate growth & other physiological processes in plants.

– Produced by root tip / shoot tip.– Affect the elongation region of the tip.


Herbicides All pesticides work by disrupting some natural

mechanism within the biology of the targeted plant, insect or animal species.– Most of these natural or man-made chemicals kill their targets.– Some protect crops or livestock by repelling pests.– The ultimate goal for pesticide researchers is to find chemicals

that kill or repel the target pests without affecting other organisms in the environment or humans.

Herbicides – chemicals that kill weeds; are the most widely used pesticides in farming.– Each year, they account for about 70 percent of all agricultural

pesticide use in the U.S.


Herbicide Groups Modern herbicides can be grouped.

1. The way they act: Herbicides are active in the weed either through contact

or in a systemic way.

2. The way they're used: Herbicides can be categorized by their use.

3. How they kill the weeds they're meant to kill: Herbicides can be classified by their mechanism of action. Herbicides work on different enzymes, proteins or

biochemical steps. Synthetic auxins

Sheryl Searcy Ninth Grade Center 2012 CONES & FLOWERS Reproduction in Seed Plants Chapter 24.

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