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Objects having characteristics of cellular organization, Growth, Reproduction, ability to sense Environment and give response are living organisms.
There are some important features of living organisms:
- It should grow, which means its structure changes as time goes by in an advantageous manner.
- It should show adaptation to the environment.
- It should maintain some balanced conditions in its inner structure. This is called Homeostasis.
- Its structure is highly organized.
- It should be able to break down or build up nutrients to release or store energy based on need. This is called Metabolism.
- It should be able to reproduce itself.
Classification of living world
The practice of classifying organisms is called taxonomy. Linneaeus developed a hierarchy of groups for taxonomy. To distinguish different levels of similarity, each classifying group, called taxon (pl. taxa) is subdivided into other groups. To remember the order, it is helpful to use a mnemonic device. The taxa in hierarchical order:
Domain – Archea, Eubacteria, Eukaryote
Archea (Archeabacteria) consists of archeabacteria, bacteria which live in extreme environments. The kingdom Archaea belongs to this domain.
Eubacteria consists of more typical bacteria found in everyday life. The kingdom Eubacteria belongs to this domain.
Eukaryote encompasses most of the world’s visible living things. The kingdoms Protists, Fungi, Plantae, and Animalia fall under this category.
Kingdom – Plantae, Animalia, Fungi, Protists, Eubacteria (Monera), Archaebacteria
Phylum
Class
Order
Family
Genus
Species : smallest classification
Cell structure and its functions
Cell is the smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.
Structure of cell
The cell is a basic unit for life forms. As well as enabling sophisticated control of biochemical processes by providing compartments and regulating chemical fluxes between them, cells also have structural Integrity and can exert forces. In the case of multicellular organisms (animals and Plants), each cell contributes some mechanical property to the tissue it forms together with other cells. Furthermore, many cells are eliminated during the life of a complex organism (e.g. skin layers in animals), which entails cell division and restructuring of the organisation with neighbours. Some types of cell are actually very motile, moving through Tissues (e.g. various immune system cells and some cancer cells). This dynamic aspect is even more obvious during the development of multicellular organisms, when many stages of cell division and Migration take place.
A first division of organisms is between those whose cells have within them a nucleus, the structure containing most of the genetic material in the form of DNA, and those whose cells don’t. The nucleated cells are called eukaryotic and are found in animals, plants, fungi, protozoa and algae. In contrast, bacteria (and the less common archaea) do not have a nucleus and their DNA is spread throughout the cell. These cells are called prokaryotic. Eukaryotic organisms can be unicellular or multicellular while all prokaryotes are unicellular.
Some of the important cell oragenells are as follows:
The Nucleus
A cell nucleus is the part of the cell which contains the genetic code, the DNA. The nucleus is small and round, and it works as the cell’s control center. It contains Chromosomes which house the DNA. The human body contains billions of cells, most of which have a nucleus. All eukaryote organisms have nuclei in their cells, even the many eukaryotes that are single-celled. Bacteria and Archaea, which are prokaryotes, are single-celled organisms of quite a different type and do not have nuclei. Cell nuclei were first found by Antonie van Leeuwenhoek in the 17th century.
The nucleus has a membrane around it but the things inside it do not. Inside it are many proteins, RNA Molecules, chromosomes and the nucleolus. In the nucleolus ribosomes are put together. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA into proteins. When a cell is dividing or preparing to divide, the chromosomes become visible with a Light Microscope. At other times when the chromosomes are not visible, the nucleolus will be visible.
Endoplasmic reticulum
The endoplasmic reticulum is a collection of interconnected tubes and flattened sacs that begin at the nucleus and ramble through the cytoplasm. There are two types of endoplasmic reticulum distinguished by the presence or absence of ribosomes.
Rough ER consists of stacked, flattened sacs with many ribosomes attached; oligosaccharide groups are attached to polypeptides as they pass through on their way to other organelles or to secretory vesicles.
Smooth ER has no ribosomes; it is the area from which vesicles carrying proteins and lipids are budded; it also inactivates harmful chemicals.
Golgi bodies
The Golgi apparatus or Golgi complex is found in most cells. It is another packaging organelle like the endoplasmic reticulum (ER). It was named after Camillo Golgi, an Italian biologist. It is pronounced GOL-JI in the same way you would say squee-gie, as soft a “G” Sound. While layers of membranes may look like the rough ER, they have a very different function.
The Golgi apparatus gathers simple molecules and combines them to make molecules that are more complex. It then takes those big molecules, packages them in vesicles, and either stores them for later use or sends them out of the cell. It is also the organelle that builds lysosomes (cell digestion machines). Golgi complexes in the plant may also create complex sugars and send them off in secretory vesicles. The vesicles are created in the same way the ER does it. The vesicles are pinched off the membranes and float through the cell.
Mitochondria
Mitochondria are rod-shaped organelles that can be considered the power generators of the cell, converting Oxygen and nutrients into adenosine triphosphate (ATP). ATP is the chemical energy “currency” of the cell that powers the cell’s metabolic activities. This process is called aerobic Respiration and is the reason animals breathe oxygen. Without mitochondria (singular, mitochondrion), higher animals would likely not exist because their cells would only be able to obtain energy from anaerobic respiration (in the absence of oxygen), a process much less efficient than aerobic respiration. In fact, mitochondria enable cells to produce 15 times more ATP than they could otherwise, and complex animals, like humans, need large amounts of energy in order to survive.
The number of mitochondria present in a cell depends upon the metabolic requirements of that cell, and may range from a single large mitochondrion to thousands of the organelles. Mitochondria, which are found in nearly all eukaryotes, including plants, animals, fungi, and protists, are large enough to be observed with a light microscope and were first discovered in the 1800s. The name of the organelles was coined to reflect the way they looked to the first scientists to observe them, stemming from the Greek words for “thread” and “granule.” For many years after their discovery, mitochondria were commonly believed to transmit hereditary information. It was not until the mid-1950s when a method for isolating the organelles intact was developed that the modern understanding of mitochondrial function was worked out.
Vesicles: There are two types of vesicles: lysosomes and Peroxisomes
Lysosomes: Lysosomes are membrane-enclosed organelles that contain an array of ENZYMES capable of breaking down all types of biological polymers—proteins, nucleic acids, Carbohydrates, and lipids. Lysosomes function as the Digestive System of the cell, serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself. In their simplest form, lysosomes are visualized as dense spherical vacuoles, but they can display considerable variation in size and shape as a result of differences in the materials that have been taken up for digestion . Lysosomes thus represent morphologically diverse organelles defined by the common function of degrading intracellular material.
Peroxisomes
Peroxisomes are small, membrane-enclosed organelles that contain enzymes involved in a variety of metabolic reactions, including several aspects of energy metabolism. Although peroxisomes are morphologically similar to lysosomes, they are assembled, like mitochondria and chloroplasts, from proteins that are synthesized on free ribosomes and then imported into peroxisomes as completed polypeptide chains. Although peroxisomes do not contain their own genomes, they are similar to mitochondria and chloroplasts in that they replicate by division.
Some specialized Plant Organelles
Plastids: There are three types of plastids: Chloroplasts, Chromoplasts, Amyloplasts
Chloroplasts are oval or disk shaped, bounded by a double membrane, and critical to the process of Photosynthesis.Chromoplasts have carotenoids, which impart red-to-yellow colors to plant parts, but no chlorophyll. Amyloplasts have no pigments; they store starch grains in plant parts such as potato tubers.
Central Vacuole
Vacuoles are essentially membrane-bound sacs found in the cytoplasm. In animal cells, vacuoles are relatively small, and are used as temporary storage areas for materials and for transport purposes. In plant cells, however, there is generally a large single central vacuole. Comprising approximately 90% of an mature plant cell, the central vacuole provides structure and support to the cell by maintaining turgor pressure, which is essentially fluid pressure that keeps the cells rigid. They are necessary to cell functions in many different ways such as maintaining cell structure and storing nutrients, waste products, and many other substances. Below is a picture of a central vacuole in a cell.
Functions of cell
Structure and support: Like a classroom is made of bricks, every organism is made of cells. While some cells such as the collenchyma and sclerenchyma are specifically meant for structural support, all cells generally provide the structural basis of all organisms. For instance, skin is made up of a number of skin cells. Vascular plants have evolved a special tissue called xylem, which is made of cells that provide structural support.
Growth: In complex organisms, tissues grow by simple multiplication of cells. This takes place through the process of mitosis in which the parent cell breaks down to form two daughter cells identical to it. Mitosis is also the process through which simpler organisms reproduce and give rise to new organisms.
Transport: Cells import nutrients to use in the various chemical processes that go on inside them. These processes produce waste a cell needs to get rid of. Small molecules such as oxygen, carbon dioxide and ethanol get across the cell membrane through the process of simple diffusion, which is regulated with a concentration gradient across the cell membrane. This is known as passive transport. However, larger molecules, such as proteins and polysaccharides, go in and out of a cell through the process of active transport in which the cell uses vesicles to excrete or absorb larger molecules.
Energy production: An organism’s survival depends upon the thousands of chemical reactions that cells carry out relentlessly. For these reactions, cells require energy. Most plants get this energy through the process of photosynthesis whereas respiration is the mechanism that provides energy to animal cells.
Metabolism: Metabolism includes all the chemical reactions that take place inside an organism to keep it alive. These reactions can be catabolic or anabolic. The process of energy production by breaking down molecules (glucose) is known as catabolism. Anabolic reactions, on the other hand, use energy to make bigger substances from simpler ones.
Reproduction: Reproduction is vital for the survival of a species. A cell helps in reproduction through the processes of mitosis (in more evolved organisms) and meiosis. In mitosis cells simply divide to form new cells. This is termed as asexual reproduction. Meiosis takes place in gametes or reproductive cells in which there is a mixing of genetic information. This causes daughter cells to be genetically different from the parent cells. Meiosis is a part of sexual reproduction.,
Cells are the basic units of life. They are the smallest living things and they are the building blocks of all living things. Cells come in many different shapes and sizes, but they all have some basic features in common.
All cells have a cell membrane. The cell membrane is a thin layer that surrounds the cell and protects it from the environment. The cell membrane is made up of lipids, which are molecules that are made up of carbon, hydrogen, and oxygen. The cell membrane is also made up of proteins, which are molecules that are made up of carbon, hydrogen, oxygen, nitrogen, and sulfur.
The cytoplasm is the jelly-like substance inside the cell membrane. The cytoplasm is made up of water, salts, proteins, and other molecules. The cytoplasm is where most of the cell’s activities take place.
The nucleus is the control center of the cell. The nucleus contains the cell’s DNA, which is the blueprint for the cell. The nucleus also contains proteins that help to control the cell’s activities.
Mitochondria are the power plants of the cell. Mitochondria produce energy for the cell. They do this by using oxygen to break down glucose, a type of sugar.
Ribosomes are the protein factories of the cell. Ribosomes make proteins. They do this by using instructions from the cell’s DNA.
Endoplasmic reticulum is a Network of membranes that helps to transport proteins and other molecules around the cell. The endoplasmic reticulum can be smooth or rough. Smooth endoplasmic reticulum is involved in the production of lipids. Rough endoplasmic reticulum is involved in the production of proteins.
Golgi apparatus is a stack of sacs that helps to modify and package proteins. The Golgi apparatus also helps to transport proteins out of the cell.
Lysosomes are sacs that contain enzymes that can break down proteins, carbohydrates, lipids, and nucleic acids. Lysosomes are involved in the cell’s defense system and in the recycling of cell parts.
Peroxisomes are sacs that contain enzymes that can break down fatty acids and other molecules. Peroxisomes also produce hydrogen peroxide, which is a substance that can be used to kill bacteria.
Vacuoles are sacs that contain water, salts, and other molecules. Vacuoles help to maintain the cell’s shape and they also help to store nutrients.
Centrioles are small, rod-shaped structures that help to organize the cell’s division. Centrioles are found in animal cells, but they are not found in plant cells.
Cilia are short, hair-like structures that help cells to move. Cilia are found on the surface of some cells, such as the cells that line the respiratory tract.
Flagella are long, whip-like structures that help cells to move. Flagella are found on the surface of some cells, such as sperm cells.
Cells are amazing and complex structures. They are the basic units of life and they are responsible for all of the activities that take place in living things.
What are the parts of an animal cell?
An animal cell is a basic unit of life that makes up all animals. It is made up of a variety of parts, each with a specific function. The main parts of an animal cell are the cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum, ribosomes, lysosomes, and vacuoles.
What is the function of the cell membrane?
The cell membrane is a thin, flexible layer that surrounds the cell. It protects the cell from its environment and controls what enters and leaves the cell.
What is the function of the cytoplasm?
The cytoplasm is the jelly-like substance inside the cell membrane. It contains all of the cell’s organelles, as well as dissolved nutrients and waste products.
What is the function of the nucleus?
The nucleus is the control center of the cell. It contains the cell’s DNA, which is the blueprint for the cell’s structure and function.
What is the function of the mitochondria?
The mitochondria are the powerhouses of the cell. They produce energy for the cell to use.
What is the function of the endoplasmic reticulum?
The endoplasmic reticulum is a network of tubules and sacs that helps to produce proteins and lipids.
What is the function of the ribosomes?
The ribosomes are the protein factories of the cell. They produce proteins from the instructions encoded in the cell’s DNA.
What is the function of the lysosomes?
The lysosomes are the cell’s garbage disposal system. They break down and recycle old or damaged cell parts.
What is the function of the vacuoles?
The vacuoles are storage sacs in the cell. They store water, nutrients, and waste products.
What are the differences between animal cells and plant cells?
Animal cells and plant cells are both eukaryotic cells, which means they have a nucleus and other organelles enclosed within a membrane. However, there are some key differences between the two types of cells.
One of the most obvious differences is that plant cells have a cell wall, while animal cells do not. The cell wall is a rigid structure that provides support and protection for the cell. Plant cells also have chloroplasts, which are organelles that capture sunlight and use it to produce food. Animal cells do not have chloroplasts.
Another difference is that animal cells have a variety of specialized structures that are not found in plant cells. For example, animal cells have cilia and flagella, which are used for movement. Animal cells also have centrioles, which are involved in cell division.
What are some examples of animal cells?
Some examples of animal cells include red blood cells, white blood cells, and muscle cells. Red blood cells are responsible for carrying oxygen throughout the body. White blood cells are responsible for fighting infection. Muscle cells are responsible for movement.
What are some diseases that can affect animal cells?
Some diseases that can affect animal cells include cancer, viruses, and bacteria. Cancer is a disease in which cells grow out of control. Viruses are tiny organisms that can infect cells and cause disease. Bacteria are single-celled organisms that can also infect cells and cause disease.
Which of the following is not a part of an animal cell?
(A) Cell membrane
(B) Nucleus
(C) Cytoplasm
(D) Cell wallThe nucleus is the control center of the cell. It contains the cell’s DNA, which is the blueprint for the cell’s structure and function.
(A) True
(B) FalseThe cytoplasm is the jelly-like substance that fills the cell. It contains organelles, which are tiny structures that carry out specific functions in the cell.
(A) True
(B) FalseThe mitochondria are the powerhouses of the cell. They produce energy for the cell to use.
(A) True
(B) FalseThe ribosomes are responsible for Protein Synthesis. They build proteins from amino acids.
(A) True
(B) FalseThe endoplasmic reticulum is a network of tubules and sacs that helps to transport materials around the cell.
(A) True
(B) FalseThe Golgi apparatus is a stack of flattened sacs that helps to package and transport proteins.
(A) True
(B) FalseThe lysosomes are sacs of enzymes that break down waste materials and old organelles.
(A) True
(B) FalseThe vacuoles are sacs that store water, food, and other materials.
(A) True
(B) FalseThe cell membrane is a thin, flexible barrier that surrounds the cell and protects it from the environment.
(A) True
(B) False