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Chapter 10: Plant Reproduction, Growth, and Development. Sexual Reproduction in Flowering Plants. Sexual reproduction requires gametes, often as egg and sperm. In flowering plants, the structures that produce the egg and sperm are located within the flower. Flower structure.
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Sexual Reproduction in Flowering Plants • Sexual reproduction requires gametes, often as egg and sperm. • In flowering plants, the structures that produce the egg and sperm are located within the flower.
Flower structure The reproductive portions of a flower are the stamen (male part), consisting of a filament and an anther, and the pistil (female part), made up of stigma, style, and ovary. Sepals enclose a whorl of petals that are usually colored to attract pollinators. The ovary contains one or more ovules.
Alternation of Generations Fig 10.1 • The sporophyte of flowering plants is dominant and produces two types of spores, microspores and megaspores.
Alternation of generations in a flowering plant Fig 10.1 The sporophyte (2N) produces haploid (N) spores by meiosis. A spore develops into a haploid gametophyte that produces gametes.
Fig 10.2 Sperm travel down the pollen tube; one sperm unites with the egg and becomes a zygote that develops into an embryo. The other sperm unites with the polar nuclei to produces triploid (3n) endosperm that nourishes the embryo. These two fusions are known as double fertilization.
The ovule wall hardens and becomes the seed coat. The seed consists of the sporophyte embryo, stored food, and a seed coat. The ovary may develop into a fruit.
Growth and Development in Plants • Development is a programmed series of stages from a simpler to a more complex form. • Cellular differentiation is specialization during development.
Development of a dicot embryo after double fertilization Fig 10.3 Becomes the Shoot Store nutrients taken from the endosperm Becomes the Stem Becomes the Root Seed Leaves
The monocot embryo has only one cotyledon that rarely stores food.
Dispersal of Seeds • Seeds are modified to be distributed far from the parent plant, by wind, animal carrier, or by ocean currents.
Germination of Seeds • Germination of seeds occurs if there is sufficient water, warmth, and oxygen to sustain growth. • Dormancy may be required before germination, and some seeds require periods of cold or minimal moisture.
Common garden bean, a dicot Fig 10.5
Corn, a monocot Fig 10.6 The coleoptile and coleorhiza are protective sheaths around the monocot plumule and radicle.
Asexual Reproduction in Flowering Plants • Non-differentiated meristem tissue allows a plant to reproduce by asexual vegetative propagation. • In horticulture, identical offspring produced by vegetative cuttings are clones.
Propagation of Plants in Tissue Culture Fig 10.7 • Plant cells are totipotent, having all the genetic potential to become mature specialized plants.
Genetic Engineering of Plants • Various techniques introduce foreign DNA into protoplasts that are propagated in tissue culture.
Control of Plant Growth and Development • Since each plant cell is totipotent, hormones have a role in determining cellular differentiation.
Plant Hormones There are five common groups of plant hormones: Auxins – promotes cell elongation andprevents growth of axillary buds (apical dominance) Gibberellins – promote growth of stems and can break seed dormancy Cytokinins – promote cell division Abscisic acid – Stress hormone Ethylene – ripens fruit and causes abscission of leaves by increasing enzyme activity
Effects of plant hormones Fig 10.9 Auxins Gibberellins
Effects of ethylene Fig 10.9
Plant Responses to Environmental Stimuli • Plant growth and development are influenced by environmental stimuli such as light, day length, gravity, and touch.
Positive phototropism Fig 10.10 Positive phototropism is due to the migration of auxin (stimulates cell elongation) from the bright side to the shady side of a stem.
Negative gravitropism Fig 10.11 In negative gravitropism, stems curve away from gravity due to auxin on the lower side of the stem.
Flowering • Short-day (long night) plants flower when the days get shorter than a critical length. • Long-day (short night) plants flower when the days get longer than a critical length. • Day-neutral plants do not depend on day length for flowering. • Phytochrome is a plant pigment believed to be involved in regulating the response of plants to day length.
Transport in the Mature Plant • Active transport concentrates minerals in root cells and xylem. • Water (and some minerals) then diffuses into the root cells and forms positive root pressure. Water and Mineral Transport in Xylem Fig. 9.8
Cohesion-tension theory of xylem transport Fig 10.15 Transpiration, evaporation of water from leaves, creates a negative pressure that pulls the water column upward. Polar water molecules are cohesive and adhere to the walls of the xylem vessel and fill the water pipeline.
Opening and Closing of Stomata Guard cells on either side of a stoma regulate its opening and closing, by changing turgor pressure.
Pressure-flow theory of phloem transport (translocation) Sugar is actively transported into sieve-tube elements and water follows passively and creates pressure . Sap moves to ‘sinks’ and sugar is actively transported out of phloem
Adaptations of Roots for Mineral Uptake • Plants are important for concentrating minerals that are used by consumers including humans.
Root nodules Bacteria in the root nodules of legumes are symbionts that convert the nitrogen in the atmosphere to NH4+.
Mycorrhizae Mycorrhizae increase water and mineral uptake and improve nutrient transfer
Epiphytes (air plants) do not grow in soil and therefore must use roots to extract moisture from air and catch rain and minerals in leaves. Parasitic plants send out root-like haustoria that tap into the xylem and phloem of the host stem.
