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why do plants produce seeds

The seed-flower life cycle

Humans have many reasons to grow plants. We use them for food, for building materials, for pleasure and for many other purposes. A plant really just has one reason to grow – to reproduce and make more plants like it! A life cycle shows how living things grow, change and reproduce themselves. Many plant life cycles include seeds. This article describes the life cycle of flowering plants.

Flowering plants grow from seeds

Flowering plants produce seeds that are then dispersed from their parent. When a seed comes to rest in an appropriate place with conditions suitable to its germination, it breaks open. The embryo inside the seed starts to grow into a seedling. Roots grow down to anchor the plant in the ground. Roots also take up water and nutrients and store food. A shoot grows skywards and develops into a stem that carries water and nutrients from the roots to the rest of the plant. The stem also supports leaves so they can collect sunlight. Leaves capture sunlight to make energy for the plant through the process of photosynthesis.

Adult plants produce flowers

When the seedling matures into an adult plant and is ready to reproduce, it develops flowers. Flowers are special structures involved in sexual reproduction, which involves both pollination and fertilisation,

Pollination

Pollination is the process by which pollen is carried (by wind or animals such as insects or birds) from the male part of a flower (the anther) to the female part (the stigma) of another or the same flower. The pollen then moves from the stigma to the female ovules.

Fertilisation

Pollen has male gametes containing half the normal chromosomes for that plant. After pollination, these gametes move to the ovule, where they combine with female gametes, which also contain half the quota of chromosomes. This process is called fertilisation. After fertilisation, the combined cell grows into an embryo inside a seed. The embryo is a tiny plant that has root, stem and leaf parts ready to grow into a new plant when conditions are right.

Length of life cycle

Flowering plants all go through the same stages of a life cycle, but the length of time they take varies widely between species. Some plants go though their complete cycle in a few weeks – others take many years.

Annuals are plants that grow from a seed. They flower, make new seeds and then die – all in less than a year. Some go through this cycle more than once in a year. Corn, beans, zinnia and marigolds are examples of annuals.

Biennials are plants that take 2 years to go through their life cycle. They grow from a seed and then rest over winter. In spring, they produce flowers, set seeds and die. New plants grow from the seeds. For example, parsley is a biennial.

Perennials are plants that live for 3 or more years. Some, such as trees, flower and set seeds every year for many years. Other types of perennials have stems and leaves that die away over winter, but the plant continues to live underground. In the spring, new stems grow, which later bear flowers. Tulips and daffodils are examples of this type of perennial.

Nature of science

Scientists often use curious terms. Sometimes the terms relate to their Greek or Latin origins. The English word ‘gamete’ refers to a reproductive cell that unites with another to form a new organism. In Greek, it is similar to the words ‘wife’, ‘husband’ and ‘to marry’.

Humans have many reasons to grow plants. We use them for food, for building materials, for pleasure and for many other purposes. A plant really just has one reason to grow – to reproduce and make more plants like it! A life cycle shows how living things grow, change and reproduce themselves. Many plant life cycles include seeds. This article describes the life cycle of flowering plants.

DK Science: Seed Plants

Most plants grow from seeds. These seed plants fall into two groups, angiosperms and gymnosperms. Angiosperms are the flowering plants. Their seeds develop inside a female reproductive part of the flower, called the ovary, which usually ripens into a protective FRUIT. Gymnosperms (conifers, Ginkgo, and cycads) do not have flowers or ovaries. Their seeds mature inside cones. Seeds may be carried away from the parent plant by wind, water, or animals.

Dandelion seeds have feathery parachutes to help them fly far from their parent plant. A dandelion flower is actually made up of many small flowers, called florets. Each develops a single fruit. The fruits form inside the closed-up seed head, after the yellow petals have withered away. When the weather is dry, the seed head opens, revealing a ball of parachutes. The slightest breeze lifts the parachutes into the air.

INSIDE A SEED

A seed is the first stage in the life cycle of a plant. Protected inside the tough seed coat, or testa, is the baby plant, called an embryo. Food, which fuels germination and growth, is either packed around the embryo or stored in special seed leaves, called cotyledons.

SPREADING WITHOUT SEEDS

Seeds are not the only means of reproduction. Some plants create offshoots of themselves – in the form of bulbs, tubers, corms, or rhizomes – that can grow into new plants. This type of reproduction is called vegetative reproduction. As only one parent plant is needed, the offspring is a clone of its parent.

A bulb is an underground bud with swollen leaf bases. Its food store allows flowers and leaves to grow quickly. New bulbs develop around the old one.

Tuber

A tuber is a swollen stem or root with buds on its surface. When conditions are right, the tuber’s food store allows the buds to grow.

A corm is a swollen underground stem that provides energy for a growing bud. After the food in the old corm is used up, a new corm forms above it.

Rhizome

A rhizome is a horizontal stem that grows underground or on the surface. It divides and produces new buds and shoots along its branches.

GERMINATION OF A RUNNER BEAN

Most seeds require damp, warm conditions in order to sprout. During germination, the seed absorbs water and the embryo starts to use its food store. A young root, or radicle, begins to grow downward. Then a young shoot, or plumule, grows upward. This develops into the stem and produces leaves. The first leaves, called seed leaves or cotyledons, fuel the early growth until the plant’s true leaves appear.

FRUITS

A flower’s ovary usually develops into a fruit to protect the seeds and help disperse them. A fruit may be succulent (fleshy) or dry. Fruit is often tasty and colourful to attract fruit-eating animals. Its seeds can pass through an animal unharmed, falling to the ground in droppings. Seeds may also be dispersed on animals’ coats, by the wind, or by the fruit bursting open.

DRY FRUITS

The seeds of dry fruits are dispersed in various ways. Peapods are dry fruits that split and shoot out their seeds by force. The hogweed fruit forms a papery wing around the seed, helping it to float on the breeze. The strawberry is a false fruit, but it is covered by tiny dry fruits, each with a seed.

SUCCULENT FRUITS

Fleshy, brightly coloured, and often scented, succulent fruits are designed to attract the animals that eat and disperse them. Fleshy fruits such as apricots and cherries have a woody stone or pip that protects the seed. Called drupes, these fruits form from a single ovary. Many drupes, formed from many ovaries, may cluster to form a compound fruit, such as a raspberry.

Most plants grow from seeds. These seed plants fall into two groups, angiosperms and gymnosperms. Angiosperms are the flowering plants. Their seeds de