Biology Unit 10 Plant Growth, Reproduction, and Response

Plant Life Cycles Alternation of generations  Plant life cycle alternates between haploid (producing gametes) and diploid (producing spores) Haploid Diploid

Plant Life Cycle Diploid phase  Begins with fertilized egg (zygote)  Zygote divides by mitosis and grows into a mature sporophyte (spore producing plant) Has specialized cells that divide by meiosis to produce haploid spores

Plant Life Cycle Haploid Phase  Spore = beginning of haploid phase  Spore divides by mitosis and grows into a gametophyte (gamete producing plant) Gamete -  When sperm meets egg, fertilization takes place and cycle continues with new sporophyte

Life Cycle of Nonvascular Plants Gametophyte phase (haploid phase) is dominant  What you are used to seeing as moss is the plant in the haploid phase Moss sporophytes are stalk-like structures that grow up from the gametophyte  Capsule at tip of sporophyte contains sporangia (spore producing sacs)  When mature the capsule opens and spores are released

Life Cycle of Nonvascular Plants Spores allow seedless plants to disperse to new areas  If spore lands in good spot for growing, it will grow into a gametophyte Moss gametophyte has special reproductive structures  Male structure produces hundreds of sperm  Female structure produces one egg When water is present sperm swim towards egg  Fertilization occurs & sporophyte phase begins again!

Life Cycle of Seedless Vascular Plants Sporophyte (diploid) is dominant phase for all vascular plants  What you are used to seeing as a fern is the plant in the sporophyte phase Underside of a fern leaf may have many sori  Clusters of sporangia (spore producing sacs)

Life Cycle of Seedless Vascular Plants Spores are released when mature Can grow into gametophyte if conditions are favorable  Prothallus – contains special structures that produce sperm and egg When water is present,sperm swim towards egg & zygote (sporophyte) forms on prothallus and grows into mature fern plant  Eventually sporophyte produces spores on the underside of each frond and the cycle begins again!

Life Cycle of Seed Plants: Conifers Sporophyte is familiar form of all seed plants Seed plants produce two types of spores that develop into male and female gametophytes  Gametophytes of seed plants are microscopic

Life Cycle of Seed Plants: Conifers Cone-bearing plants have male and female cones  Female cones are larger and more scaly than male cones  Female cones grow for several years & contain two ovules that produce spores One spore in each ovule develops into female gametophyte  Male cones only live a few weeks Spores develop into pollen grains (male gametophytes)

Life Cycle of Seed Plants: Conifers Male cones release clouds of pollen When pollen lands on female cone it sticks Pollination = when pollen grain reaches an ovule  Eggs produced inside ovule  Pollen tube forms from pollen grain to egg In pine trees takes 1 year to reach the egg 2 sperm develop in pollen grain, travel down pollen tube to reach egg Fertilization occurs & ovule develops into protective pine seed Seed released → life cycle starts over with new sporophyte (pine seedling)

Life Cycle of Seed Plants: Conifer 2 sperm develop in pollen grain, travel down pollen tube to reach egg Fertilization occurs & ovule develops into protective pine seed Seed released → life cycle starts over with new sporophyte (pine seedling)

Reproduction in Flowering Plants Flowers contain reproductive organs protected by specialized leaves  Can be green or brightly colored Bright colors help attract animal pollinators  Sepals – modified leaves the protect the developing flower  Petals – layer inside the sepals, also modified leaves

Reproduction in Flowering Plants Most flowers have both male and female structures  Stamen = male structure Each stamen has a stalk that supports an anther Anthers produce pollen grains (male gametophytes)

Reproduction in Flowering Plants  Carpel = female structure Innermost layer of the flower Most flowers have several carpels fused together forming a pistil 3 parts of carpel:  Stigma = tip of carpel, covered with a sticky substance that holds pollen grains when they land there.  Style = tube that leads from stigma to ovary  Ovary = at base of flower, produces female gametophytes

Pollination in Flowering Plants Plants can be pollinated by wind or by animals Animal pollination is more efficient Wind pollinated species have small flowers and lots of pollen Animals pollinate by vising the flower to feed and getting dusted by pollen grains. As the animal goes to another flower to get food, pollen from the first flower brushes against the stigma of the other flower

Fertilization in Flowering Plants Fertilization takes place in the flower Production of male gametophytes – cells within the anthers divide by meiosis to produce 4 male spores Each spore divides again by mitosis forming 2 cells (sperm) Theses 2 cells together with thick wall for protections = pollen grain Production of female gametophytes One female gametophyte can form in each ovule of a flower's ovary

Fertilization in Flowering Plants Double Fertilization One sperm cell fertilizes egg Other sperm cell becomes endosperm (food supply for developing plant embryo) Only happens in flowering plants

Seeds and fruit At fertilization, next sporophyte generation begins Ovule becomes a seed Embryo + endosperm While seed develops, surrounding ovary grows into fruit Fruit aids in dispersal of seeds to new areas Each seed has the ability to grow into a mature plant

Seed Dispersal and Germination Animals, wind, and water can spread seeds. Fruits come in a variety of shapes and sizes

Seed Dispersal and Germination Seeds can travel to new location with wind or water Coconuts can travel thousands of miles across oceans Seeds can be eaten by animals and the undigested seeds are dropped off in a new location with plenty of fertilizer

Seed Dispersal and Germination Seeds begin to grow when environmental conditions are favorable Seeds can be dormant for thousands of years During dormancy, embryo stops growing Seeds begin to grow when there are certain changes in temperature, moisture, or light levels

Seed Dispersal and Germination During germination the embryo breaks out of the seed coat and begins to grow into a seedling Embryo takes up water Water causes the seed to swell and crack Embryonic root breaks through the crack as it grows Young shoot eventually breaks through the surface of the soil

Asexual Reproduction Plants can reproduce asexually with stems, leaves, or roots Allows well adapted plant to make copies of itself Most plants have a way of cloning themselves through asexual reproduction Regeneration – growing a new plant from a fragment of a stem, leaf, or root

Asexual Reproduction Vegetative reproduction – stems, leaves, or roots attached to the parent plant produce new individuals potato

Plant Hormones Plant hormones regulate plant functions Hormone = chemical messenger produced in one part of an organism that controls the activity of cells in another part

Plant Hormones Gibberellins – produce dramatic increases in size End seed dormancy Start germination Promote rapid growth of young seedlings Makes fruit larger

Ethylene – causes ripening of fruits Auxins – stimulate growth of the primary stem Cytokinins – stimulate cytokinesis (final stage of cell division) Produced in growing roots and developing seeds and fruits Also involved in growth of side branches

Plant Responses Tropism – movement of plants in response to environmental stimuli Phototropism – plant grows towards light

Plant Responses Gravitropism – upward and downward growth of a plant due to gravity –Downward growth (roots) = positive gravitropism –Upward growth (shoots) = negative gravitropism Thigmotropism – plant response to touch –Climbing plants and vines –Venus flytrap

Plant Responses Photoperiodism – plants respond to changing days and nights throughout the year (seasonal changes)