Intoducing... DIFFUSION!

What is it?
It is the random movement of molecules of a substance from a region of higher concentration to a region of lower concentration down the concentration gradient.

IMPORTANCE OF DIFFUSION

• Living organisms obtain many of their requirements and get rid of their toxic metabolic products by diffusion.
• Plants need carbon dioxide for photosynthesis and carbon dioxide molecules requires diffusion to enter the leaf through the stomata.
• Oxygen, a waste product of photosynthesis diffuses out the leaves by diffusion.
• Respiration in animals require oxygen. Oxygen in inhaled air dissolves in the moisture lining the alveoli of the lungs, then moves through the walls of the alveoli into the blood by diffusion.
• Some of the end products of digestion or nutrients are absorbed from the ileum of mammals by diffusion.
• Absorption of some mineral nutrients by roots.

The Red Blood Cells

FUNCTION

• To absorb and transport oxygen from the lungs to body tissues

ADAPTATION TO FUNCTION

• Contain a red pigment called haemoglobin which is a protein molecule containing iron. In the lungs, the oxygen diffuses with the haemoglobin to form oxyhaemoglobin which is bright red. When it reaches a tissue, which needs oxygen, the oxyhaemoglobin gives up the oxygen to form haemoglobin again. Therefore haemoglobin enables the red blood cell to transport oxygen from the lungs to the body tissues.
• Red blood cells do not contain nuclei. Absence of the nucleus results in the red blood cell being circular and biconcave disc in shape. This increases the surface area to volume ratio so that oxygen can diffuse into or out of the whole cell at a faster rate. Therefore the rate of absorption and release of oxygen is faster.
• Red blood cells are extremely small and large in numbers and so have a very large total surface area for oxygen absorption making it a very efficient process.
• Red blood cells are flexible. they can become bell-shaped and so can pass along very narrow capillaries. This also decreases the rate of blood flow through the capillaries thus providing more time and increasing the efficiency for gaseous exchange.

The Root Hair Cell

FUNCTIONS

• Responsible for the absorption of water from the water film surrounding the soil particles by osmosis.
• Allow simple diffusion of dissolved mineral salts in the soil solution to pass into the root hair. This is only possible if a concentration gradient is present (ie if such minerals in the salt in the soil water are in greater concentration than in the root hair cell)
• The root hair cells absorb minerals that are present in low concentration in the soil by active transport.

ADAPTATION TO FUNCTION

• The root hair cell is able to form very close contact with the water film surrounding many soil particles. This allows rapid and efficient absorption of water from the soil.
• The root hair cell is long and narrow. This increases the surface area to volume ratio of the cell for rapid absorption of water and mineral salts from the soil.
• The cytoplasm and cell sap of root hair cells contains a high concentration of sugars, amino acids and mineral salts. Water in the soil therefore diffuses into the root hairs, down the water potential gradient, through the partially permeable cell membrane into the vacuole by osmosis.

Let's get to know more about cells!

ALL cells have the following structural features in common:

• PROTOPLASM
• Protoplasm is the mass of living matter. 
• It is a complex jelly like substance of which 70-90% is water while the rest consists of mineral salts, organic compounds, etc. 
• Chemical reactions take place here.
• Protoplasm is a collective term for cell membrane, cytoplasm and nucleus.

• CELL MEMBRANE
• It is present in all plants and animal cells.
• It completely surrounds the call and holds in the constituents of the cell.
• It is a thin living structure that encloses the entire cell.
• It provides a high surface area for the absorption of nutrients and the disposal of wastes.
• It is a partially permeable membrane.
• It controls substances entering and leaving the cell.
• It stops cell contents from escaping. Small substances such as oxygen, water, glucose and other simple food substances are allowed to enter. Waste products are allowed to leave the cell and harmful substances are kept out. Large molecules like proteins are not able to leave the cell.
• It is a two-layered structure. The outer and inner layers are made of proteins and the region in between them contains a double layer of lipids (fats). This gives the cell its characteristic shape.
• Acids and heat can denature it.

• CYTOPLASM
• A jelly like substance where chemical or metabolic reactions of the cell take place
• It is the basic living material of all cells
• It is a complex mixture of chemicals of which 70-90% is water. 
• the main contents of the cytoplasm are proteins, fats, carbohydrates, mineral salts and digested food substances such as glucose and amino acids.

• NUCLEUS
• It is a spherical or oval body lying in the cytoplasm.
• It is present in all plant and animal cells.
• It contains a hereditary material known as chromosomes that are made of the chemical DNA (deoxyribonucleic acid) which is organised into genes and controls all cellular activities of the cell.

• RIBOSOMES
• They are very tiny round organelles present in the cytoplasm
• They are responsible for the synthesis of proteins from amino acids

• MITOCHONDRIA
• Mitochondria (singular : mitochondrion) are tiny, spherical or sausage or rod-shaped organelles present in plant and animal cells. 
• They are often called the power houses of the cell.
• They are most numerous in regions of rapid chemical activity (eg muscles).
• They are responsible for producing energy by oxidising food substances in a process known as aerobic respiration. the energy released can be used by the cell to perform vital activities (eg cell division, growth or respiration)

PLANT cells have the following additional structures:

• A LARGE CENTRAL VACUOLE
• Younger plant cells have very tiny vacuoles.
• Mature plant cells have a large fluid filled space called a vacuole. Animal cells have much smaller vacuoles which may contain food and water.
• A vacuole is a space in a cell surrounded by a membrane known as the tonoplast
• A vacuole contains cell sap, a solution made up of mostly sugars, mineral salts and amino acids and other substances including waste products.
• The vacuole is sometimes called the "sap vacuole".
• Vacuoles play an important role in osmosis.

• THE CELLULOSE CELL WALL
• The plant cell is completely enclosed by a non-living cell wall made of cellulose (a polysaccharide)
• Animal cells do not have cell walls
• Cellulose form fibres that criss-cross over each other to form a very strong covering of the cell.
• This helps to protect and support the cell. 
• The spaces between the fibres allow very large molecules to pass through the cellulose cell wall. It is therefore said to be fully permeable.
• It allows water and dissolved food substances to pass through.

IF the cell is involved in the process of photosynthesis, then it also contains:

• CHLOROPLASTS
• Chloroplasts are never found in animal cells.
• They are only present in plant ccells that perform photosythesis.
• They can be located in the cytoplasm.
• They are green in colour because they contain thee green pigment, chlorophyll, which absorbs sunlight.
• The light energy from the sun, plus carbon dioxide and water is the used for making glucose by photosynthesis.

Introduction to CELLS

Cells can be defined as the simplest unit of life. Cells can also be defined as the structural and functional units of organisms.The cell is the smallest unit of life. Often cells are microscopic and not visible to the human eye.

 Even though the cell is tiny, there are many parts to a living cell. Animal cells are different from plant cells. There are no cell walls or chloroplasts in animal cells.

Unlike the animal cells, plant cells have cell walls made of cellulose and chloroplasts containing chlorophyll for photosynthesis.

8 Characteristics of Most Living Things (MERIGRAN)

M - MOVEMENT (LOCOMOTION)

Most animals move their whole bodies using their limbs.
Plants move only by growing part of theirselves towards or away from influences important to them (light, sounds, touch, temperature, etc.)

E - EXCRETION

It is the process involving the removal of metabolic waste products (such as carbon dioxide, water, mineral salts and nitrogenous waste products). These substances can be useless or harmful and so must be removed from the body of the organism.

R - REPRODUCTION

This process involves the production of an offspring (or offsprings). This process is necessary for the species to survive.

I - IRRITABILITY (COORDINATION & RESPONSE)

Organisms can sense and respond appropriately to any changes in the immediate surroundings (light, temperature, etc.). They react to these changes in a way beneficial to themselves (folding of Mimosa leaves when touched, growth of plants towards the light).

G - GROWTH

Growth is an increase in the cell numbers, size, dry mass or volume of an organism as a result of converting absorbed food into living protoplasm. This may make the organism more complex or even change its form (egg of a butterfly becoming a caterpillar, germination of a seed into a seedling, etc.)

R - RESPIRATION

It is the oxidation of food substances with the release of energy in living cells. The energy released is used for movement, growth, reproduction, etc.

A - ADAPTABILITY (HOMEOSTASIS)

Organisms have the ability to adjust and adapt themselves to changes in their environment. This adaptability increases their chances of survival and the preservation of their own species.

N - NUTRITION (FEEDING)

This is the process in which living things take in food substances and convert them into the living protoplasm of the organism.

An introduction to Biology

What is Biology?
The term biology comes from the Greek Language : bios means life and logos means knowledge.
Therefore biology can be defined as an organised study of living things.