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Biology Terms A - L.

posted Jul 17, 2015, 8:07 PM by Upali Salpadoru   [ updated Sep 14, 2017, 2:36 PM ]
  • Abiogenesis

Non living matter getting organized into living matter.


Characteristics of organisms that improve their chances of survival. For more click

Plant adaptations.

  • Adipose tissue

Closely packed fat cells found under the skin and around some organs such as the heart.

  • ADP

Adenosine Di Phosphate.  ATP gets converted to this when energy is released.

  • Algae  

These are plant cells having a cell wall and a nucleus and chlorophyll to produce food. They lack specialised structures like stomata. Specimens range from Chlamydomonas and Spirogyra to very long seaweeds called Kelp.

  • Allele.
  • Different forms of a gene resulting from mutation and are placed at a specific place in a chromosome.
1. Recessive allele- These lie dormant unless the same is present in genes inherited from mother and the father.
2. Dominent Allele-These become functional even if present only in one copy.
  • Altruism

Certain type of animal behaviour to protect their young ones. The parent trying to attract a predator to save young ones.

  • Apostosis

A living cell may die in two ways. It may die due to adverse conditions such as extreme temperature , harmful substances or injury. This is called Necrosis. The other method is the ‘Programmed death’. When the services of a cell no longer required, or if it has gone out of control or when there is DNA damage it gets programmed to disintegrate and break up. The broken pieces are quickly cleansed by the macrophages. This method of cell suicide is called apostosis.

  • Antibodies

Proteins produced by the immune system which mark foreign matter so that they may be destroyed.

  • Antigen

A protein labelled by an antibody.

  • ATP

Adenosine Tri Phosphate. The molecule that supplies energy in muscles.

  • Aves

The group to which the birds belong.

  • Axil

The angle between the leaf stem and the branch. Go to Parts of a plant

  • Axillary bud

Every axil of a plant is capable of  producing a growing or a flower bud.    

  • Alimentary Canal.

Al can.jpg

A form that a gene can take.

  • Amino acid

These are the building blocks of proteins. There are 20 amino acids that are essential for us. We can synthesize only 10 of these in our body. Even when one is absent proteins cannot be made. Unlike carbohydrates and fats amino acids cannot be stored in our body

  • Amoebiosis

Intestinal disease caused by a protozoan Endamoeba.

  • Antibody

When a germ or a virus enters the body a type of white blood cells produce these proteins in order to destroy them.

  • Auxin

A growth hormone produced in plants.


  • Bacteria

 A very important group of microscopic living things, unicellular with a cell wall which is not made of cellulose. They are unable to make food as they lack chlorophyll. There are beneficial bacteria as well as harmful bacteria called germs.

  • Bacteriophage

     A virus that attacks bacteria.

  • Bile

A yellow green alkaline fluid secreted by the liver and stored in the gall bladder. Released to emulsify fat to help digestion.

  • Biodiversity

Vast variety of life forms found in a particular environment.

  • Bio engineering.

Application of engineering techniques in biology or medicine. It may also mean application of biological processes in industry.

  • Bio fuel

Fuel obtained from living things excluding fossil fuel. Eg. Vegetable oils that may be used as diesel.

  • Biome

The total complex of living species occupying a particular zone.

  • Biosphere

All strata in the planet where living things are found.

  • Bone

The skeleton of vertebrates consist of bones. They are semi rigid tissue consisting of bone cells, osteocytes, mainly made up of of calcium salts. Blood is made in the bone marrow.

  • Brain


  • Black smokers.

In 1976 researchers working in the east Pacific Ocean made an astounding discovery. Several hot water (hydrothermal) vents were found at the mid-ocean ridge on the bottom of the ocean. The vents were pumping superheated, black, mineral-rich fluids into the sea, and these ‘black smokers’ were home to unique and bizarre forms of life. Professor Alexander Malahoff, now Chief Executive of GNS Science, was one of the first people to study black smokers. Three decades later, another New Zealand scientist, Dr Cornel de Ronde, proved that black smokers also appear on the summits of underwater volcanoes above seduction zones..............Auckland war. memorial museum.

  • Blood

Constituents in blood.

1. Blood plasma

This is 90% water with dissolved gases along with sodium and potassium ions. Nutrients and hormones. The blood cells are suspended in the fluid. Some white cells can even creep out of the blood vessels..

2.Red Blood Cells   RBC.  (Erythrocytes)

These have done away with their nuclei in order to give room for haemoglobin to transport oxygen. The spleen breaks down these cells after a service of 3 to 4 months. There are about 5 million RBC / microliter.

3.White Blood Cells WBC.  (Leucocytes)

This can be considered as the army of our body that attack invaders such as germs and other unwanted microorganisms. They are nucleated cells that live only for a few days. In a normal person there are about 7000/microliter which may increase in times of need.

4.Platelets (Thrombocytes)

These are un nucleated cells that can live only for a few days. In case of an external injury and the blood is exposed to air. Aided by vitamin K and calcium they stick together forming a web of fibrinogen preventing the loss of blood. These are generally known as clots. If they are formed inside due to some reason it is called ‘thrombosis’.

  • Blood Circulation.

Blood C.jpg

There is a highly sophisticated system of arteries, veins and capillaries to transport the blood from the heart to various parts of the body.

  • Blood groups

According to the AB0 blood group system there are four different kinds of blood groups: A, B, AB and 0.

Courtsey:- American Red Cross.
In 1827 Robert Brown (1773–1858), the Scottish botanist,  had observed that pollen grains floating in water move in a zig zag motion.   


·         Callus

Plant cells that cover a wounded portion of a plant.
  • Carbon- Oxygen cycle.
Blue lines show the path of Oxygen while the black is for Carbon dioxide.

·         Central nervous system

This includes the brain and the spinal cord. It controls all sensory activities of the body.

·         Cerebellum

Located just above the brain stem and is concerned with muscle control and balance.

·         Cerebrum

This is the largest part of the human brain situated at the top of the head just below the skull. It consists of two hemispheres and is responsible for perception and intelligence.

·         Cell

This name has been given by Robert Hook who examined a piece of dead cork.  This really is the unit of life .  Every cell in an organism is a miniature of the whole. That means entire genetic system is encoded in every cell.

All living things are made up of cells. Although viruses show some characteristics of life as they do not have cells they are excluded from the category of living things.


Parts of Eukaryotic cells

1.Cell wall

This is present only in plants, bacteria and fungi. Plant cell walls are made of cellulose. This maintains the shape of the cell and counter acts pressure when it absorbs water.

2.Cell membrane  

This envelops the cell contents of all cells. This is the outermost layer in animal cells.  Being a highly specialized organ this can select what molecules or ions pass through. Animal cells are capable of changing shape due to the flexibility of this.


This is the fluid, with dissolved and suspended matter that fills the cell. Buried in this medium are the ‘Organelles’. (small organs)


These are separated from the ‘cytosol’ by double layered membranes and carry out specialized functions.


Fig. Structure of the nucleus.


As it is concerned with cellular respiration it is called the ‘power house’ unlike other organelles this has its own set of genes. Hence come on the maternal line. A copy of this is found only in egg cells but not in sperms.

While this is absent in bacteria, which are termed ‘Prokaryotes’ other organisms,’ Eukaryotes’ protect all genetic material inside this.

7.Endoplasmic reticulum

Major centres for the synthesis of proteins and lipids essential for the cell.

8.Golgi bodies

Mainly concerned with preparing the molecules to be sent out of the cell or to be used inside.


Cylindrical structures present only in animal cells. They organise the micro filaments that forms the cytoskeleton.  There is a pair of centrioles that move to opposite ends during cell division.


Concerned with the cytoskeleton. They also help to move certain molecules 

  • Cell division

There are two ways by which cells can divide. They are Meiosis and Mitosis

·         Chromatid

A chromosome consists of two identical units joined at the centromere which dis engage for cell division. Any one of these is termed a chromatid.

·         Chromosome

Each chromosome is made up of DNA tightly coiled around proteins called histones. They become visible , even through a microscope, only when they are dividing. At cell division they are present in pairs connected at a point called a centromere. Every organism has a definite number of chromosomes. A human cell has 23 pairs.

  • Commensalism

In this type of association one party benefits and the other gets neither benefit nor harm.


  • Descent  

Change in the genetic composition of a population during successive generations, often resulting in the development of new species. The mechanisms of evolution include natural selection acting on the genetic variation among individuals, mutation, migration, and genetic drift.

  • Digestion

This is the process by which large molecules of food, are converted to simpler, water soluble molecules inside the digestive tract (Alimentary canal). The process includes physical, such as chewing and churning and chemical reactions such as due to gastric enzymes. Broadly speaking there are three broad categories of digestion.

Internal digestion- Inside cells as in amoeba. Food is taken into a food vacuole and digested.

There are two types of External digestion.

1.    In fungi digestive juices are poured into the food and only the digested food is absorbed into the cells.

2.    In higher animals there is a gastric canal in which digestion takes place. This happens outside the cells.

  • Diffusion

This is the spreading of molecules in a gas or a liquid. The net result of mixing is always moving from higher concentration to lower concentration. Oxygen enters the blood by diffusion. In the plant leaves diffusion of gases take place through the stomata.   Go to Speed of a molecule.

Dialysis and Osmosis are special cases of diffusion. Osmosis is using a semi permeable membrane to separate two solutions involved in diffusion such as passing of the solvent without the solute. Dialysis is the application of this process to purify the blood in cases of kidney failiure.

  • DNA


Deoxy ribonucleic acid. This may be considered as a polymer of nucleotides. Within cells these are organized into chromosomes. The discovery of Frederich Miescher in the nineteenth century and the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin  a century later was the biggest break in the study of biology since the theory of evolution.


  • Enzyme. These are organic catalysts secreted by various glands in the body.
  • Eukaryotes

 The most structurally complex cell type of cells, They contain smaller interior compartments, that are enclosed by lipid membranes similar to outermost cell membrane.

This is the theory accepted by the scientists that all living things had a common ancestor. Those believe that man was created find it difficult to believe this.
  • Excretion
This is the elimination of waste products formed inside the cells of living organisms. 


  • Flower


Fig. Parts of a dicotyledonous flower.

These may be the most beautiful creations of nature. They are borne only in certain plants called ‘angiosperms’. Ferns and conifers do not flower. The flowers of monocots are trimerous  ( sets of 3) while the flowers are pentamerous  (sets of  5).


This holds the flower out of the bush to welcome visitors.


Several whorls are attached to this base. Sometimes there is a nectary too.

3.Calyx-These are like small leaves, called sepals that cover up the floral parts during bud stage. This is absent in primitive flowers like ‘magnolia’.

4.Corolla-The most  colourful whorl consisting of petals which may be soft, smooth or velvety and usually scented. Some have lines to guide the pollinator to the nectary and drop the pollen on to them.

5.Androecium-Consists of antherlobes attached to the receptacle with long filaments. Pollen grains are produced in the anthers which are shed on maturity. These  are similar to animal sex cells though produced in slightly a different way.

6.Gynoecium-This is the female organ of the flower, pistil. That houses the ovules which develop into seeds after fertilization. The ovary becomes the fruit.

  • Fossil

These are preserved specimens from a past geologic age. Even a foot print of an ancient animal may be considered as a fossil.  Coal and Petroleum are considered as fossil fuels.


  • Gamete

A mature sex cell which is produced by reduction division that can unite with another of the opposite sex in sexual reproduction to form a zygote. There are isogametes as well as male and female gametes.

  • Gene
  • A gene is a location in the DNA molecule, where information is recorded to make a particular protein that will carry a certain trait. 

  • Genome.

This is a set of DNA, including all the genes. Each genome contains the entire information needed to build and maintain that organism. In humans, a copy of the genome has more than 3 billion DNA units. They are  contained in every normal  cell.

  • Giberalin

A plant hormone especially concerned with stem elongation bud development after winter.

  • Glomerulus

A small convoluted or intertwined mass; a tuft of capillaries at the origin of each nephron that passes the filtrate to the surrounding Bowman's capsule. As the blood flows through the glomerulus, some  plasma passes through the glomerular membrane,, and then flows through the renal tubules. Much of this fluid passes back into the blood via the small capillaries around the tubules .


  • Habitat

The natural environment in which a species or group of species lives. 

  • Haploid

Having one set of chromosomes as in sex cells. (Other cells are diploid)

  • Hypothalamus.

A section of the brain responsible for the production of many of the body’s essential hormones, chemical substances that help control different cells and organs. The hormones
Body temperature
Appetite and weight control
Sleep cycles
Sex drive


  • Inflammation
          This is the reaction produced in the body in order to counteract the harmful effects of a pathogen.
  • Inheritance

The process of genetic transmission of characteristics from parent or ancestor to offspring The sum of genetically transmitted characteristics..

  • Iris  
This is the coloured part of the eye that controls the size of the aperture (opening known as pupil)


  • Joint

A junction between two bones. These bear weight and permit bending. Eg. Hnee joint.


  • Knee joint and Knee jerk.

  • Knee jerk
A reflex contraction of the quadriceps muscle resulting in a sudden involuntary extension of the leg, produced by a sharp   tap to the tendon below the patella; patellar reflex. courtsey :- The free dictionary.

  • Kidneys

A pair of organs at the back of the abdomen. Each is about 12 cm. long. They remove the nitrogenous waste ma

erials from the blood and maintain the equilibrium of electrolytes. Nephrons remove urine which passes through the ureter to the bladder.

  • Kinesis

An animal's non-directional movement to a stimulus, 

  • Kingdoms

All living organisms have been divided into prokaryotes and Eukaryotes and they are again sub divided into 5 kingdoms. Prokaryotic cells have no organelles. Eukaryotes have organelles leading of which is the nucleus.




                            No organelles

1.Archaea , blue green algae.





All are considered prokaryotes. Contains bacteria and blue-green algae

2.Protista - Protozoans and some algae.


Consists of cells made of chitin, uni-cellular or multicellular often multi nucleated. No chlorophyll and saprophytic

4.Plantae- Manufactures food using light due to presence of chlorophyll. Cells are bounded by cell walls made of ‘cellulose’.

5.Animalia- Depends on other living things for food as chlorophyll is absent. Extremely mobile due to lack of cell walls.

L a

  • Nucleus