Plant Growth, Reproduction, and Response Unit 10

Plant Life Cycles

Plant Life Cycle Plant life cycles alternate between producing spores and gametes. The plant life cycle in which the plant alternates between haploid (1n) and diploid (2n) phases is called alternation of generations.

Plant Life Cycle The diploid phase of a plant life cycle begins with a fertilized egg, called a zygote. A zygote divides by mitosis and grows into a mature sporophyte, or spore-producing plant. A spore makes the beginning of the haploid phase of the plant life cycle. A spore divides by mitosis and grows into a mature gametophyte, or gamete-producing plant.

Plant Life Cycle

Plant Life Cycle

Plant Life Cycle NOTE: Mitosis can occur in haploid cells as well as diploid ones. A haploid set of chromosomes, and hence a single set of genes, is sufficient to control cell function in these organisms (but not in most animals). The gametophyte generation is the major stage in the life of mosses and an independent plant in ferns.

Life Cycle of Nonvascular Plants: Moss gametophyte phase is dominant sporophytes are stalk-like structures that grow up from the gametophyte capsule at tip of moss sporophyte contains spore-producing sacs called sporangia when mature, capsule opens  spores released

Life Cycle of Nonvascular Plants: Moss moss gametophyte produces gametes male: sperm (many) female: egg (1) sperm swim toward egg if water is present  fertilization after fertilization, sporophyte phase begins once again

Life Cycle of Nonvascular Plants: Moss

Life Cycle of Seedless Vascular Plants: Ferns sporophyte is dominant phase (for all vascular plants) underside of a fern leaf (frond)  sori clusters of sporangia (spore-producing sacs) spores released when mature can develop into a gametophyte if conditions are favorable for growing

Life Cycle of Seedless Vascular Plants: Ferns prothallus: fern gametophyte (about the size of your little fingernail anchors to soil with tiny threadlike structures called rhizoids contains special reproductive structures that produce sperm and eggs

Life Cycle of Seedless Vascular Plants: Ferns If freestanding water is present, male structures release sperm sperm swim  egg  fertilization zygote forms on the prothallus beginning of sporophyte generation Zygote grows above prothallus  mature sporophyte fiddleheads: newly forming fronds

Life Cycle of Seedless Vascular Plants: Ferns

Life Cycle of Seed Plants: Conifers sporophyte: familiar form (for all seed plants) seed plants produce two types of spores that develop  male and female gametophytes gametophytes of seed plants are microscopic

Life Cycle of Seed Plants: Conifers Example: pine tree branches have two different types of cones (male & female) female cones  larger and more scaly; live and grow for several years each scale of a female pinecone: 2 ovules that produce spores 1 spore/ovule  gametophyte male cones live only for a few weeks male spores  pollen grains (male gametophyte)

Life Cycle of Seed Plants: Conifers male cones release clouds of pollen in the spring pollen grain lands on a female cone, sticks pollination: pollen grain reaches opening of ovule. eggs are produced inside the ovule pollen tube begins to grow from pollen grain  egg In pine species, it takes a year for pollen tube to reach egg

Life Cycle of Seed Plants: Conifers 2 sperm develop inside pollen grain travel down pollen tube toward egg no flagella (don’t need to swim through water to reach egg) 1 sperm may fertilize an egg  zygote  embryo ovule  protective pine seed each scale: 2 developing pine seeds when seeds mature, scales open up and release them life cycle starts over w/new sporophyte (pine tree seedling)

Life Cycle of Seed Plants: Conifers

Take Home Message All plants alternate between two phases in their life cycles. Plant life cycles alternate between producing spores and gametes. Life cycle phases look different among various plant groups.

Reproduction in Flowering Plants

Reproduction in Flowering Plants Flowers contain reproductive organs protected by specialized leaves. The outermost layer of a flower is made up of sepals – modified leaves that protect the developing flower. The layer inside the sepals is made up of petals, which are modified leaves. protect reproductive structures attract pollinators

Reproduction in Flowering Plants

Reproduction in Flowering Plants Some species have flowers with only male or only female structures, but the flowers of most species have BOTH.

Reproduction in Flowering Plants male part of a flower: stamen filament supports anther, which produces pollen grains (male gametophytes) female (inner) part of a flower: carpel several carpals fused together form pistil female gametophytes are produced inside the ovary (at base of flower)

Reproduction in Flowering Plants

Reproduction in Flowering Plants Pollination  wind or animals (more reliable) Insects, birds, and animals that visit flowers collect pollen as a food source. When the animal searches for food in another flower, pollen from the first flower brushes against the stigma of another flower.

Reproduction in Flowering Plants

Reproduction in Flowering Plants

Reproduction in Flowering Plants Fertilization takes place within the flower. Anthers produce pollen grains (male gametophyte) Cells w/in anthers divide by meiosis  4 spores Spores divide by mitosis  2 haploid cells Along with protective these 2 cells form a pollen grain

Reproduction in Flowering Plants Fertilization takes place within the flower. One cell in ovule divides by meiosis to form 4 spores (3 usually die) Remaining spore divides 3 times to form embryo sac (female gametophyte) One large, central cell has 2 haploid polar nuclei One of the other cells develops  egg

Reproduction in Flowering Plants Double Fertilization After pollination, one cell in pollen grain grows into a pollen tube Extends down style  ovule Other cell in pollen grain divides by mitosis  2 sperm Both travel down pollen tube One sperm fertilizes egg Other sperm combines w/polar nuclei in embryo sac

Reproduction in Flowering Plants Double Fertilization The sperm cell that does NOT fertilize the egg has a triploid (3n) nucleus and becomes the endosperm, a food supply for the developing plant embryo. Only happens in flowering plants!

Reproduction in Flowering Plants

Reproduction in Flowering Plants – Animation Double Fertilization

Flowering Plants Life Cycle A tomato plant is a typical flowering plant. If the flower is pollinated and fertilization occurs, ovules will develop into seeds and the surrounding ovary will develop into a fruit.

Flowering Plants Life Cycle

Flowering Plants Life Cycle

Flowering Plants Life Cycle

Flowering Plants Life Cycle

Seeds and Fruit At fertilization, ovule becomes a seed embryo nutritious endosperm protective seed coat

Seeds and Fruit Using nutrients provided by endosperm, embryo develops 1-2 cotyledons, which sometimes provide nourishment for the new plant before it can begin producing its own food through photosynthesis

Seeds and Fruit While the seed develops, the surrounding ovary grows into a fruit. Flowering plants that produce many seeds w/in 1 ovary – larger fruit

Seeds and Fruit After a pumpkin flower (left) is pollinated and fertilization occurs, seeds and fruit begin to develop. The pumpkin fruit (center) is green at first, containing immature seeds. The ripe fruit (right) is orange and contains mature pumpkin seeds.

Seed Dispersal and Germination Animals, wind, and water can spread seeds. Recall that when a seed develops, the surrounding ovary grows into a fruit. Animals eat the fruit, and use their ‘waste’ as fertilizer (with the undigested seed inside), to make new seed plants.

Seed Dispersal and Germination

Seed Dispersal and Germination Seeds begin to grown when environmental conditions are favorable. When a seed is dormant, or under dormancy, the embryo stops growing. This happens if the temperature, moisture, oxygen, and/or light levels are not favorable to the seed.

Seed Dispersal and Germination Many types of seeds begin to grow when there are certain changes in temperature, moisture, or light levels. 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 plant is free of seed coats and grows!

Asexual Reproduction Plants can that can grow a new individual from a fragment of a stem, leaf, or root are reproducing by regeneration. Most plants have a way of cloning themselves through asexual reproduction.

Asexual Reproduction Humans can produce plants with desirable traits using vegetative structures. Example: seedless fruit

Plant Hormones and Responses Plant hormones regulate plant functions. A hormone is a chemical messenger produced in one part of an organism that stimulates or suppresses the activity of cells in another part. In humans, hormones control functions vital to survival and reproduction. In plants, when a hormone meets the right receptor, it triggers a response.

Plant Hormones and Responses

Plant Hormones and Responses Types of plant hormones and their functions: Gibberellins – produce increase in size in plants Ethylene – causes ripening in fruits Cytokinins – stimulate cytokinesis, the final stage of cell division Auxins – lengthening of plant cells

Plant Hormones and Responses Phototrophism – tendency of plant to grow towards light (light) Thigmotrophism – plants response to touch (touch) Gravitrophism – up-and-down growth of plant due to Earth’s gravitational pull (gravity) Photoperiodism – plants response to changing of days and night throughout the year (season changes)

Plant Hormones and Responses

Take Home Message Reproduction of flowering plants takes place within flowers. Flowers contain reproductive organs protected by specialized leaves. Flowering plants can be pollinated by wind or animals. Fertilization takes place within the flower.