CELL AND ITS ENVIRONMENT

Environment/Nature and State of Matter

Living cells are known to be surrounded by a watery environment. This may include: Fresh/salt water in which the unicellular organisms live, Intercellular fluid that bath the bodies of cells of higher animals.

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The nature of states of matter makes diffusion and osmosis possible.

Matter can be defined as any material that has mass and occupies space. It includes all the living and non-living things around us. Matter is also made up of tiny particles which may be molecules or irons and can exist in three forms; solid, liquid, and gas.

DIFFUSION

Diffusion is the process by which molecules of substances move from a region of higher concentration to a region of lower concentration (through the medium of air or liquid) until equilibrium is reached. The difference in the concentration of the substances in the two regions before diffusion occurs is called concentration/diffusion gradient, e.g. If KMn04 (Potassium tetraoxomanganate VII) is placed in a beaker of water and allowed to stand, the purple colour of the KMn04 start to spread outward from the crystal. Eventually, the colour spread evenly throughout the water medium.

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Diffusion is also observed in the spread of odour of perfume, insecticide which is used to spray a room and also in the release of gases from the anus.

Diffusion is affected by the following factors

Change in temperature: The higher the temperature, the faster the rate of diffusion
Molecular size: Diffusion increases with decreasing size of molecule
State of matter Diffusion of gases is much faster than that of liquid.
Difference in concentration: The greater the difference in concentration of molecules, the faster the rate of diffusion.

IMPORTANCE OF DIFFUSION IN LIVING ORGANISMS

The movement of carbon (IV) oxide through the stomata of leaves during the process of photosynthesis.
Movement of oxygen into the leaves during respiration.
Movement of water vapour out of the leaf in the process of transpiration
Gaseous exchange in the lungs of mammals
Intake of oxygen and nutrients and the removal of waste product by the foetus from its mother through placenta.
Movement of digested and soluble food from the villi of small intestine to the blood stream.
Removal of waste product in small organisms such as amoeba

OSMOSIS

Osmosis can be defined as the movement of water molecules from a region of lower concentration to the region of higher concentration through a semi-permeable membrane.

A permeable membrane allows molecules to pass through it freely while a selectively permeable membrane only allows certain molecules to pass through it. Osmosis will only occur when a semi-permeable membrane separates weak and strong solutions.

Living cells may find themselves in any of the following situation:

When the fluid surrounding the cell is more concentrated than the inside of the cell, the surrounding fluid is said to be hypertonic to the content of the cells. A net movement of water molecules out of the cell into the surrounding fluid occurs and causes the cell to shrink. This process is known as
When the fluid surrounding the cell is less concentrated than the inside of the cell, the surrounding fluid is said to be hypotonic to the content of the cell. There is a net movement of water molecules from the surrounding fluid into the cells. This process is known as
When the surrounding fluid and the cell concentration have the same concentration, they are said to be Isotonic. A net movement of water molecule in and out of the cells does not occur.

IMPORTANCE OF OSMOSIS

It aids the absorption of water from the soil into the vacuole of the root hairs
It aids the movement of water from the root hairs into the cells of other parts of the plants
It helps to control the opening and closing of the stomata pores
It gives turgidity to the plant cells i.e. it gives support.
It aids intracellular movement of water in animals
It aids reabsorption of water from the kidney tubules into the blood
It causes haemolysis of red blood cells.

PLASMOLYSIS

Plasymolysis is the shrinkage of the vacuole and pulling away of the cytoplasmic lining from the cell wall when placed in hypertonic solution. When a plant cell is surrounded or place in hypertonic solution, exosmosis will occur i.e. water moves out of the cell into the surrounding fluid leading to the shrinking of the vacuole and pulling the cytoplasm away from the cell wall. When cells are plasmolysed, it eventually leads to wilting or death of the plant.

HAEMOLYSIS

This is the process whereby red blood cells (corpuscles) splits and burst as a result of too much water passing into it. Red blood cells and blood plasma are always isotonic i.e. having the same osmotic concentration, if for some reasons the concentration of blood plasma falls; endosmosis will occur (water moves from the plasma into the red blood cells). Continuous absorption of water into the cell makes it turgid and when fully stretched, it burst.

TURGIDITY AND BIOLOGY SIGNIFICANCE

Turgidity is the condition in which cell absorbs plenty of water up to a point where the cell is fully stretched. Turgidity is observed in plants where it makes them erect and support the stem, leaves and flowers.

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FLACCIDITY AND BIOLOGICAL SIGNIFICANCE

Flaccidity is the condition in which plant lose water to their surrounding faster than they can absorb. When a plant loses more water than it absorbs, it becomes flaccid. Flaccidity usually occurs when there is no water in the soil, especially where there is drought. The continuous loss of water can result in the death of the plant.