Chapter 24 Reproduction of Seed Plants

24-1: ALTERNATION OF GENERATIONS

• All plants have a life cycle in which a diploid sporophyte alternates with a haploid gametophyte.
• Gametophyte plants produce male and female gametes—sperm and eggs.
• When the gametes join, they form a zygote that begins the next sporophyte generation.
• In some plants, the two stages of the life cycle are distinct, independent plants.
• The gametophytes of seed plants are hidden deep within tissues of the sporophyte plant.

LIFE CYCLE OF GYMNOSPERMS

• Gymnosperms are diploid sporophytes.
• Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant.
• Gymnosperms produce two types of cones: pollen cones and seed cones.

Life Cycle of Gymnosperms: POLLEN CONES & SEED CONES

• Pollen cones are male cones. Seed cones, which produce female gametophytes, are much larger.
• Pollen cones produce the male gametophytes, which are called pollen grains.
• The pollen grain makes up the entire male gametophyte stage of the gymnosperm life cycle.
• Near the base of each scale are two ovules in which the female gametophytes develop.
• When mature, each gametophyte contains a few large egg cells, each ready for fertilization.

Life Cycle of Gymnosperms: FERTILIZATION AND DEVELOPMENT

• When a pollen grain lands near an ovule, the grain splits open and begins to grow a pollen tube.
• Once the pollen tube reaches the female gametophyte, one sperm nucleus disintegrates.
• If sperm from another pollen tube reaches the female gametophyte, more than one egg cell may be fertilized.

STRUCTURE OF FLOWERS: SEPALS AND PETALS

• Flowers are made from four kinds of special leaves: sepals, petals, stamens, and carpels.
• The outermost parts contains the sepals, which in plants are green and closely resemble ordinary leaves.
• Sepals enclose the bud before it opens, and they protect the flower while it is developing.
• Petals, which are often brightly colored, are found just inside the sepals. ​Petals attract insects.
• The sepals and petals of a flower are sometimes called sterile leaves.

STRUCTURE OF FLOWERS: STAMENS & CARPELS

• Within the ring of petals are the structures that produce male and female gametophytes.
• The male parts consist of an anther and a filament, that make up the stamen. ​It supports an anther.
• At the tip of each filament is an anther, an oval sac where meiosis takes place, producing pollen grains.
• Each carpel has a broad base forming an ovary, where female gametophytes are produced.
• A typical flower produces both male and female gametophytes.

LIFE CYCLE OF ANGIOSPERMS

• Reproduction in angiosperms takes place in the flower. Following pollination and fertilization.
• Embryo Sac: female gametophyte within the ovule of a flowering plant.
• In the ovary, cells of the growing embryo differentiate, specialize, and develop.

POLLINATION

• Once the gametophytes have developed inside the flower, pollenation begins.
• Most gymnosperms and some angiosperms are wind pollinated.
• These animals, mainly insects, birds and bats carry pollen flower to flower.
• Wind pollination is less efficient than animal pollination.
• Pollen grains are caught in a sticky secretion on one of the scales of the female cone.

FERTILIZATION of Angiosperms

• If a pollen grain lands on the stigma of an appropiate flower of the same species, it begins to grow a pollen tube.
• Pollen tube: a hollow tube that develops from a pollen grain when deposited on the stigma of a flower.
• Endosperm: food-rich tissue that nourishes a seedling as it grows.
• Double fertilization: fertilization in angiosperms; two fertilization events take place between male and female.

24-2: SEED DEVELOPMENT AND GERMINATION

• As seeds mature, the ovary walls thicken to form a fruit that encloses the developing seed.
• After Fertilization, nutrients support the development of the growing seed within the embryo.

SEED DISPERSAL

• Animals eat fleshy fruit, then release the seeds in their feces at a distance from the parent tree.
• Some examples are apples, blueberries, and blackberries.
• Lightweight seeds, such as maple, is spun by the wind to a different location.

SEED DORMANCY

• Enviromental factors such as temperature and moisture can cause a seed end to end dormancy and germinate.
• Dormancy: an alive embryo that does not grow.
• Adaption because of dormancy: long distance dispersal, germination in ideal weather.
• This is such that plants survive in the Winter and sprout in the Spring.

24-3:PLANT PROPAGATION & AGRICULTURE

• Vegetative Reproduction: how flowering plants reproduce asexually.
• Through Mitosis, vegetative reproduction allows one plant to produce offspring genetically identical.
• New plants can be produced from horizontal stems, plantlets, and underground roots.
• Horizontal stems: plants send long stems, stolons, which produce roots when they touch the ground.
• Plantlets: many angiosperms produce small plants at the tip of long stems.

PLANT PROPAGATION

• Plant propagation: cutting, grafting, or budding to make identical copies of a plant or produce offspring.
• Cutting: the grower cuts a plants length of stem with a number of buds that contain meristematic tissue.
• Grafting: when stems are used in scions and then grown on the stock. (the plant to which it is attached)
• Budding: when buds are used as scions and grown on the stock.

AGRICULTURE

• Agriculture: the systematic cultivation of plants; an extremely old process used for more than 12,000.
• Most of the people of the world depend on a few plants, wheat, rice and corn for the bulk of their food supply.
• Almost all plants that are raised for food are angiosperms; new plants have changed human history.
• By breeding crops that produce more, many have doubled or tripled the amount of edible material they produce.
• Pesticides and fertilizers have contributed to dramatic improvements in the fields.