Science
Growth in plants and humans
All animal and plant cells have a nucleus, cytoplasm and a cell membrane. Plant cells also have a cell wall, chloroplasts and a vacuole. Different parts of the cell are adapted to perform different functions.
Humans grow at different rates at different stages in their lives. Gestation and infancy are the times of fastest growth.
Growth
Plant and animal cells
All animals and plants are made of cells. Animal cells and plant cells have features in common, such as a nucleus, cytoplasm and cell membrane. Plant cells also have a cell wall, chloroplasts and a large vacuole.
Cell functions in all cells
| Part | Function |
|---|---|
| Nucleus | Contains genetic material (DNA) which controls the activities of the cell |
| Cytoplasm | Contains enzymes and other chemicals – it's the site of most cell processes and reactions |
| Cell membrane | Regulates the movement of material into and out of the cell |
Cell functions in plant cells
| Part | Function |
|---|---|
| Cell wall | Supports the cell, made of cellulose |
| Chloroplast | Absorbs light energy and uses it to produce sugars in photosynthesis. Chloroplasts mainly found in leaf cells. |
| Large vacuole | Provides support by exerting pressure on the cell contents. Contains a solution of minerals and other nutrients. |
Growth in plants and animals - higher only
Plants and animals grow and differentiate their tissues in different ways. The main differences are outlined in the table below.
Growth in plants and animals
| Feature | Plant | Animal |
|---|---|---|
| Where growth occurs | Mainly at shoot and root tips and in special growth zones like buds | New cells can be made by most tissues |
| How growth occurs | Size increase often caused by increasing the size of cells by absorbing water into the vacuole | Size increase is brought about by increasing the number of cells |
| Cell specialisation | Most plant cells can differentiate into different cell types | Only stem cells can differentiate into different cell types. Other animal cell functions remain fixed. |
Stem cells are undifferentiated cells found in animals, that have the ability to grow into different tissues. They offer a possible cure for many diseases caused by cell damage. Some people object to research using stem cells that have been taken from embryos. Other sources of stem cells are umbilical cords and bone marrow.
Growth in humans
Humans grow at different rates at different stages in their lives. Growth is very rapid in the womb and in the first two years of life. Puberty is another stage when growth and development is rapid.
Growth in humans
| Stage | Time | Growth | Care |
|---|---|---|---|
| Gestation | 40 weeks before birth | Very fast | All requirements obtained via placenta |
| Infancy | Birth to 2 years | Fast | Dependent on others for food and care |
| Childhood | 3-10 years | Steady growth and mental development | Becoming independent |
| Adolescence | 11-17 years | Growth spurt, puberty, mental development | Increasingly independent |
| Adulthood | 18-60 years | Peak health and fitness but no increase in height | Independent |
| Old age | 60 years to death | Some tissue degeneration | Increasingly dependent |
Human gestation is around 40 weeks although infants can survive if born earlier than this. Other mammals have different gestation times depending on their size, the number of offspring and how independent they are when born. Large animals with a small number of independent offspring have the longest gestation.
When humans are born, their heads are relatively large, and their legs relatively short. Through childhood their bodies grow faster than their heads until they reach maturity. To check that development is happening at normal rates, infants regularly have their mass and head circumference measured.
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