Nov 17, 2011

Facts about cell

Cells are the fundamental units of life. Whether they be unicellular or multicellular life forms, all living organisms are composed of and depend on cells to function normally. Scientists estimate that our bodies contain anywhere from 75 to 100 trillion cells. Cells do everything from providing structure and stability to providing energy and a means of reproduction for an organism. The following facts about cells will provide you with well known and perhaps little known tidbits of information about cells.

1. Cells are too small to be seen without magnification.
Cells range in size from 1 to 100 micrometers. The study of cells, also called cell biology would not have been possible without the invention of the microscope. With the advance microscopes of today such as the Scanning Electron Microscope and Transmission Electron Microscope, cell biologists are able to obtain detailed images of the smallest of cell structures.

2. There are two primary types of cells.
Eukaryotic and prokaryotic cells are the two main types of cells. Eukaryotic cells are called so because they have a true nucleus. Animals, plants, fungi and protists are examples of organisms that are composed of eukaryotic cells. Prokaryotes include bacteria and archaeans.

3. Prokaryotic single-celled organisms were the earliest and most primitive forms of life on earth.
Prokaryotes can live in environments that would be deadly to most other organisms. They are able to live and thrive in various extreme habitats. Archaeans for example, live in areas such as hydrothermal vents, hot springs, swamps, wetlands, and even animal intestines.

4. There are more bacterial cells in the body than human cells.
Scientists have estimated that about 95% of all the cells in the body are bacteria. The vast majority of these microbes can be found within the digetive tract.

5. Cells contain genetic material.
Cells contain DNA (deoxyribonucleic acid), the genetic information necessary for directing cellular activities. DNA is a type of molecule known as a nucleic acid. In prokaryotic cells, the single bacterial DNA molecule is not separated from the rest of the cell but coiled up in a region of the cytoplasm called the nucleoid region. In eukaryotic cells, DNA molecules are located within the cell's nucleus. DNA and proteins are the major components of chromosomes. Human cells contain 23 pairs of chromosomes (for a total of 46). There are 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. The X and Y sex chromosomes determine gender.

6. Cells contain structures called organelles which carry out specific functions.
Organelles have a wide range of responsibilities within a cell that include everything from providing energy to producing hormones and enzymes. Eukaryotic cells contain several types of organelles, while prokaryotic cells contain a few organelles (ribosomes) and none that are bound by a membrane. There are also differences between the kinds of organelles found within different eukaryotic cell types. Plant cells for example, contain structures such as a cell wall and chloroplasts that are not found in animal cells. Other examples of organelles include:
  • Nucleus
  • Mitochondria
  • Endoplasmic Reticulum
  • Golgi Complex
  • Ribosomes
7. Different types of cells reproduce through different methods.
Most prokaryotic cells reproduce by a process called binary fission. This is a type of cloning process in which two identical cells are derived from a single cell. Eukaryotic organisms have a similar type of reproductive method known as mitosis. Some eukaryotes also have the ability to reproduce sexually, which involves the fusion of sex cells or gametes. Gametes are produced by a process called meiosis.

8. Groups of similar cells form tissues.
Tissues are groups of cells with both a shared structure and function. Cells that make up animal tissues are sometimes woven together with extracellular fibers and are occasionally held together by a sticky substance that coats the cells. Different types of tissues can also be arranged together to form organs. Groups of organs can in turn form organ systems.

9. Cells have varying life spans.
Cells within the human body have different life spans based on the type and function of the cell. They can live anywhere from a few days to a year. Certain cells of the digestive tract live for only a few days, while some immune system cells can live for up to six weeks. Pancreatic cells can live for as long as a year.

10. Cells commit suicide.
When a cell becomes damaged or undergoes some type of infection, it will self destruct by a process called apoptosis. Apoptosis works to ensure proper development and to keep the body's natural process of mitosis in check. A cell's inability to undergo apoptosis can result in the development of cancer.

Nov 4, 2011

Respiration in Plants

Plants also respire aerobically to obtain energy for metabolism. They derive most energy from cellular respiration.
During cellular respiration, energy is obtained by breaking down glucose. The energy released is stored in ATP molecules.
Although plants cannot photosynthesise without sunlight, respiration continues because plants need energy constantly to sustain vital living processes.

Gaseous exchange between plant cells and the environment occurs by diffusion mainly through the stomata and lenticels. Respiratory gases enter and leave plants via stomata in the epidermis of the leaves and the stems of herbaceous plants. Lenticels are raised pores found on the stems and roots of plants.

When stomata are open, they connect the air spaces within the leaves to the atmosphere.
Oxygen from the atmosphere diffuses into the air spaces and then dissolves in the film of water around the mesophyll cells.
Oxygen is then used in aerobic respiration.
The concentration of oxygen in the cells becomes lower than the concentration of oxygen in the air spaces.
The difference in concentration gradient allows oxygen to diffuse continuously from the air spaces into the cells.
During the day, the carbon dioxide which is produced during aerobic respiration is used in photosynthesis.
The excess carbon dioxide diffuses into the air spaces and then through the stomata into the atmosphere.
Aerobic respiration is usually carried out by all plants throughout the day and night.
However, under certain conditions, plants can carry out anaerobic respiration for short periods.
For example, in flood. 
Anaerobic respiration also occurs during initial stages of seed germination.
Respiration and photosynthesis are interdependent. Photosynthesis produces the raw materials required by respiration and respiration produces the raw materials required by photosynthesis.

As light intensity increases during the day, the rate of photosynthesis also increases. Eventually a point reached at which all carbon dioxide produced during respiration is used in photosynthesis. At this point, there is no net gain or net loss in the sugar produced. The plant has reached a compensation point.
The compensation point is the light intensity at which the rate of carbon dioxide production during respiration is equal to the carbon dioxide consumption during photosynthesis.

As light intensity continues to increase during the day, the rate of photosynthesis exceeds the rate of respiration. The carbon dioxide produced during respiration is no longer sufficient fro the plants. Plants must take in carbon dioxide from the atmosphere to supplement the need for a higher concentration of carbon dioxide during photosynthesis. At the same time plants release the excess oxygen into the atmosphere.