Plant Reproduction & Response to the Environment

Seeds A plant structure that contains an embryo, contains nutrients for the embryo, and is covered with a protective coat These features enable seeds to survive harsh environmental conditions and then sprout when favorable conditions exist.

Seeds Seeds have one or more cotyledons that store or help absorb food for the sporophyte. Plants whose seeds are part of fruits are called angiosperms (flowing plants) Plants whose seeds are not part of fruits are called gymnosperms (non-flowering plants)

Alternation of Generations Gametophyte (haploid)generation produces gametes. Sporophyte (diploid)generation produces spores that can grow to form the next gametophyte generation. Gametophyte generation—maple pollen Sporophyte generation—maple tree

Alternation of Generations Diploid sporophyte generation alternates with a haploid gametophyte generation Gametophyte of gymnosperms are in the cones, and in angiosperms they are in the flowers

Reproduction in Gymnosperms Two types of cones: Pollen cone (male cone) – produce pollen Seed cone (female cone) – contains the ovules, where the eggs are held Pollination – transfer of pollen from the male structure to the female structure Fertilization and development then occur

Reproduction in Gymnosperms

Reproduction in Angiosperms Occurs in the flower Most angiosperms are pollinated by animals (insects, birds) Double fertilization One sperm fertilizes the egg and becomes the zygote A second sperm fertilizes the embryo sac and becomes the food supply

Reproduction in Angiosperms

Reproduction in Angiosperms The ovary becomes the fruit Seeds are dispersed by animals, wind, and water Germination – early growth of the plant

Germination

Structure of a Flower Sepals – enclose the bud Petals – attract pollinators Stamen – male structure Filament – long, thin stalk that supports the anther Anther – produces pollen Carpels (or pistils) – female structure Ovary – contains the ovules Style – stalk of the carpel Stigma – sticky surface where pollen lands

Structure of a Flower

Asexual Reproduction Vegetative reproduction – production of new plants from stems, leafs, and roots Cutting – pieces of plant cut off and planted Grafting & budding – a stem or bud is cut from one plant & attached to another

Plant Hormones Auxins – stimulate cell elongation Cytokinins – stimulate cell division Gibberellins – produce increases in size Ethylene – stimulates fruit to ripen

Plant Responses Tropisms – responses of plants to environmental stimuli Gravitropism – response to gravity Phototropism – response to light Thigmotropism – response to touch Positive – in the direction of the stimulus Negative – away from the stimulus

Plant Responses