Supplying the Cell

Diffusion

Cells cannot always rely on the passive movement of chemical via osmosis and diffusion. There are many situations when a cell or an organism needs to move chemicals against the diffusion gradient, from an area of low concentration to an area of high concentration. Root cells in a plant are in this situation. The minerals and salts in the soil around the roots are in much lower concentrations than they are in the cytoplasm of the cells. This would mean that diffusion will try to move the minerals from the plant back into the soil. To overcome this problem cells use active transport. __This process uses energy from the cells to pump chemicals from one place to another. __

Unlike osmosis and diffusion, active transport requires energy from respiration, but it gives the cell control over the direction of movement and the speed of movement of chemicals.

The cell membrane has a series of protein molecules along its length that can temporarily bind with key molecules, like minerals. They can rotate to move these molecules into or out of the cell when needed. This motion needs energy, but the cell controls this movement.

Osmosis

__Mitosis is the process by which a cell is able to make a copy of itself. __This is used in single cell organisms for reproduction and in multicellular organisms for growth and repair.

For a cell to make a copy of itself it must also copy all of its genetic code in the form of its chromosomes, as well as physically divide the structure of the cell.

At the end of the growth and rest phase when the cell is ready to replicate, it starts by pulling its long strands of DNA into chromosomes. At this point, the chromosomes are visible under a light microscope. The chromosomes replicate making an identical copy of themselves. These line up along the middle of the cell and proteins strands develop to attach each copy of the chromosomes to opposite sides of the cell. The cell pulls the chromosomes apart and begins to divide by pulling in its cell membrane to create two new cells. These daughter cells contain the same DNA as the original parent cell, they are clones of the original cell. They then spend some time growing before they can divide again.

The growth phase between divisions varies a great deal between organisms, some bacteria can undergo mitosis every 15 to 20 minutes. This gives them the ability to reproduce very rapidly. Some adult human cells may not divide for weeks unless they are needed for repair.

Active Transport

Stems cells are undifferentiated cells that have the capability to divide and produce new differentiated cells for the purposes of growth and repair. They are the ‘stock’ of basic template cells that can then be adapted to make a more specialist cell. There two types of stem cells, embryonic stem cells and adults (somatic) stem cells.

Embryonic stem cells are found in the tissues of a developing fetus in the womb, these cells are capable of differentiating into any type of cell within the body. Embryonic stem cells are of special interest to medical research, their capability to regenerate into any cell might lead to curse for a number for degenerative disorders included motor neuron disease and Parkinson’s disease.

Adults stem cells in animals are found throughout the body. Although they are often called ‘adult’ stem cells they are found in the body at all ages of life. They are responsible for growth, repair and replacement of damaged and dying cells. Unlike embryonic stem cells, adult stem cells can only differentiate into a limited number of cell types. Stem cells in the bone marrow of the upper thigh, for example, can divide to make replacement red blood cells, but they can not become muscle or nerves etc.

Plants also have adults stem cells, but they are found only at the growing points at the tips of the stem and roots and at nodes along the stem seen as a bud. The main growing point at the top of a stem is called the apical meristem and the side shoots and buds are called the axillary meristems.

The movement of water into a cell is due to the process of?

osmosis

State how this cell is differentiated to aid this function.

Your answer should include: long extension to the cell membrane to stick out into the soil give a large surface area / large vacuole for storage of minerals

Minerals in the soil are in a lower concentration than they are in the root hair cells, how do cells uptake minerals against this concentration gradient, explain how the cell membrane aids in this process

active transport

Stem cells in embryos are of interest to medical science, but there are groups of people that think it is not ethical to use this material for research. Explain why the researchers do not just use adult stem cells for their research.

the stems cells from adults can only differentiate into a limited number of cells whereas the stem cells from embryonic tissue can differentiate into all the cell types in the body