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’.
