The Fundamental Unit Of Life

Both living and non-living organisms are highly different from each other. Living is anything which is made up of cells while non-living is formed by elements, particles, chemicals etc. For example: Humans, animals, insects, plants all are living organisms, they have complex biological makeup of cells but fan, table, refrigerator etc are all machines the non-living which work by performing physical and chemical reactions. But from where do they get the energy? Both living and non-living require energy to do their specific function but the energy for living comes from food like plants prepare their own food, and utilize it, humans animals feed on plant and animal as they are their source of food. Similarly machines get their energy from fuel, oil, electricity etc. Hence the similarity is that they both require energy to carry out their work.

The nucleus is also called as brain of the cell. It contains the genetic material within itself, i.e. DNA (Deoxy-ribonucleic acid) which codes the genetic information of a living entity. It is the largest organelle within the cell. It is present in the eukaryotic cell but is absent in prokaryotic cell, because of which they can be highly distinguished. It has its own covering which separates it from its surrounding cytoplasm called the nuclear envelope. Also, the envelope has certain small pores which regulate the exchange of materials like protein, RNA, etc between the cytoplasm and nucleus. It has chromatin material within the cell consisting of thin long threads of DNA encircled around protein. It is responsible for the transfer of Character from parent to offspring via genetic material (DNA) present inside the nucleus.

Plastids are double membrane bound organelles found only in plant cells and algae. Their main function is processing and storing food inside the cell and can be used up by the cell in the condition of stress. Plastids are of three different types, but chloroplast among them is solely responsible for carrying out photosynthesis.

Chloroplasts: These are the highly abundant plastids found in plants. They are responsible for carrying out the major process of food preparation called photosynthesis. A chloroplast is a disc shape organelle within a plant cell which allows plants to capture the Sun energy in energy-rich molecules. Both chloroplast and mitochondria evolved from an independent free-living prokaryote, hence they share similar functions.

Chloroplasts are surrounded by two membranes, i.e. bilayered. It is made of phospholipids. The outer membrane is more permeable to small organic molecules, whereas the inner membrane is less permeable and has transport proteins embedded in it. The innermost matrix of chloroplasts is called stroma.

Chloroplasts also have an internal membrane called the thylakoid membrane which contains the light-harvesting complex, including pigments, as well as the electron transport chains which is used in photosynthesis. Each chloroplast contains a green-colored pigment called chlorophyll which is required to carry out the process of photosynthesis. The chlorophyll pigment absorbs sunlight and uses it to transform carbon dioxide (CO₂) and water (H₂O) into glucose, which will be used up in further processes like respiration.

Plant cell do not contain centrosomes, they are only found in animal cells. Their main function is to form the microtubules in the nucleus which attach to chromosomes for their equal distributions during cell division. While other organelles are found in plant cells with their specific functions:

• Chloroplast performs photosynthesis.

• Vacuoles are store house of food and nutrients. They are of larger size in plant cells.

• Mitochondria help in generating energy for the cell by producing ATP.

• Nucleus contains the genetic material and assists protein synthesis.

• Cell wall provides mechanical strength to the plant cell.

Animal cell do not contain cell wall and chloroplast, they are only found in plant cells. Chloroplast carries out photosynthesis which id required for food generation. Cell wall provides mechanical strength to the plant cell thus protecting it from the harsh environmental conditions. While other organelles are found in both plant and animal cells with their specific functions:

• Vacuoles are store house of food and nutrients. They are of larger size in plant cells.

• Mitochondria help in generating energy for the cell by producing ATP.

• Nucleus contains the genetic material and assists protein synthesis.

Golgi apparatus is the organelle in eukaryotic organisms which is concerned with cell secretions. Their whole structure is made up of membranes with some vesicles at the outside. Their main function is to transfer/movement of the molecules from either away from endoplasmic reticulum or towards it. They are highly involved in secretion of hormones, steroids and various other proteinaceous substances This process occur via formation of vesicles, that are of two types: endocytosis and exocytosis. At the end these vesicles fuse with the plasma membrane and release the continent outside the cell.

Mitochondria also known as power house of the cell is a double membrane bound organelle. It has its own cytoplasm called mitochondrial matrix which has suspended ribosome and DNA. This mitochondria generate energy in the form of adenosine triphosphate (ATP). This ATP is used by ribosome to form proteins after the transcription of DNA.

Ribosome’s are called the ribonucleoprotein particles in a cell. They are called so, because they are formed by association of both RNA and protein. They suspend freely in the cytoplasm and gets stuck to the walls of endoplasmic reticulum as they get the signal from the nucleus. After the signal they carry out the process of protein synthesis via translation.

Lysosomes are one of the membrane bound organelles which are present in both plant and animal cells. There membrane is also made up of phospholipids. This membrane protects the cell from the hydrolytic enzymes of lysosomes. This organelle present inside the plant cell is most important for the process of digestion and excretion. It contains various digestive enzymes which digest the damaged and worn out organelles, bacteria’s, viruses etc. They are also called as “suicidal bags” or “garbage disposable units” of a cell by De Duve. They contain more than 50 hydrolytic enzymes which can breakdown and digest various molecules. Their fluid content has acidic pH approximately equal to 5, due to the presence of digestive enzymes.

The centrioles inside the animal cells form the asters of spindle. These centrioles are found within the centrosome which gives rise to microtubules. Asters are the star-shaped microtubules formed inside the nucleus. They are present at two corners of an animal cell during the process of mitosis in cell division. They attach themselves to the chromosomes via spindle fibers for the equal segregation of the number of chromosomes in the dividing cells.

Cells are fluid filled balloons having an outer membrane. Their fluid spaces contain organelles, enzymes and chemicals. Cells are the smallest entity within a living cell. It is the structural and functional part of all living organisms because this small unit itself contains the identity of the whole organism. So we can say all living like dog, cat, human, horse, insects have multiple cells having multiple specific functions. These cells perform all the biological and metabolically processes which are required for the proper functioning of organisms.

• They maintain their structure by maintaining the turgor pressure inside the cell.

• They process their own food, process it into energy and eliminate waste as well.

• They reproduce continuously by cell division, so that the organism won’t die. For example in humans the life span of RBCs (red blood cells) is of120 days, so this means after 120 days we should die, but this doesn’t happen because cells keep on dividing simultaneously and maintain their number in our body.

The plant cell is of rectangular shape and is comparatively bigger than the animal cell. Both plant and animal cells are eukaryotic cells and they have few similar cell organelles. But plant cell differ from animal cell by the presence of a cell wall outside the cell membrane.

Cell wall provides strength, protection against mechanical and osmotic stress to the plant cell and to provide form and structure to the cell. Cell develops turgor pressure against the cell wall. When there is a healthy supply of water, a plant is protected from wilting due to this turgor pressure.

Plant cell walls are made of cellulose, glycoproteins, lignin, pectin, and hemicelluloses. The formation of the cell wall is done by microtubules. It consists of three layers called as primary, secondary and the middle lamella. The primary cell wall is mainly formed by cellulose laid down by various enzymes.

As cell is the basic unit of life, similarly genes are the basic unit of living organisms. They provide traits or characteristics to organisms that pass on from generation to generation. These are nucleotide sequences of DNA or RNA which encodes the genetic information. There are different numbers of genes in different species. For example: humans have 25,000 genes in its genome, E.coli (bacteria) has 5,500 genes and Arabidopsis thaliana (plant) has almost 25,500 genes in their genomes. Since genes are made of DNA, they can also be called as unit of heredity. This double helix structure encodes the basic instructions of living organisms. This is the reason why children have characteristics similar to their parents, as this nucleic acid passed down from generation after generation with multiple modifications thus distinguishing you a bit from your parents. It recites inside the nucleus of a cell. This twisted staircase structure is made up of four nitrogenous bases: Adenine (A), guanine (G), cytosine (C) and thymine (T). It is composed of de-oxyrisbose sugar. It was discovered by James Watson and Francis Crick. This genetic material is enclosed in a nuclear envelope of only eukaryotes and the two membranes bound organelles called mitochondria and chloroplast. They are not protected by a nuclear envelope in prokaryotic organisms. But RNA is the genetic material of viruses.

Genes determine the character of organism; they can affect specific traits through any mutation via external or internal environment. These mutations are a result of distinguished traits among individuals. Sometimes these mutations can be negative which can affect the health of organisms. Causing some diseases, such as sickle-cell anemia and Huntington's disease, and since genes are heritable it will cause the disease to be inherited as well.

Everything in the world is made up of elements, but nucleic acids are made up of only 5 elements. These are Oxygen (O), Hydrogen (H), Nitrogen (N), Carbon (C) and Phosphorus (P). These elements combine into specific orientations and give rise to genetic material of living organisms. These two nucleic acids are:

i. DNA (deoxyribonucleic acid): This double helix structure encodes the basic instructions of living organisms. This is the reason why children have characteristics similar to their parents, as this nucleic acid passed down from generation after generation with multiple modifications thus distinguishing you a bit from your parents. It recites inside the nucleus of a cell. This twisted staircase structure is made up of four nitrogenous bases: Adenine (A), guanine (G), cytosine (C) and thymine (T). It is composed of deoxyrisbose sugar. It was discovered by James Watson and Francis Crick. This genetic material is enclosed in a nuclear envelope of only eukaryotes and the two membranes bound organelles called mitochondria and chloroplast. They are not protected by a nuclear envelope in prokaryotic organisms.

ii. RNA (ribonucleic acid): It is the genetic material of viruses. This RNA has major role in protein synthesis inside a cell. Their structure is also made up of four nitrogenous bases: Adenine (A), guanine (G), cytosine (C) and Uracil (U). Here thymine is replaced by uracil. Another difference between RNA and DNA is that RNA is single stranded. It was discovered by Friedrich Miescher. It is composed of ribose sugar. RNA is of three types:

• rRNA (ribosomal RNA) which do protein synthesis.

• mRNA (messenger RNA) which transfer code from DNA to the nucleus for rRNA to do its work.

• And, tRNA (transfer RNA) carries various amino acids to ribosomes.

Plastids are double membrane bound organelles found only in plant cells and algae. Their main function is processing and storing food inside the cell and can be used up by the cell in the condition of stress. Plastids are of three different types:

(a) Chromoplasts: These are color plastids which provide a color to different parts of plants like flowers, fruits etc. These colors are due to pigments stored in them.

(b) Leucoplasts: These are colorless plastids. They are found in such parts of plants which are incapable of doing photosynthesis like roots. They also used for fatty acid and amino acid synthesis.

(c) Chloroplasts: These are the highly abundant plastids found in plants. They are responsible for carrying out the major process of food preparation called photosynthesis. A chloroplast is a disc shape organelle within a plant cell which allows plants to capture the Sun energy in energy-rich molecules. Both chloroplast and mitochondria evolved from an independent free-living prokaryote, hence they share similar functions.

Chloroplasts are surrounded by two membranes, i.e. bilayered. It is made of phospholipids. The outer membrane is more permeable to small organic molecules, whereas the inner membrane is less permeable and has transport proteins embedded in it. The innermost matrix of chloroplasts is called stroma. It contains metabolic enzymes and multiple copies of the chloroplast genetic material in the form of a circular DNA.

Chloroplasts also have an internal membrane called the thylakoid membrane. It contains the light-harvesting complex, including pigments, as well as the electron transport chains which is used in photosynthesis. Each chloroplast contains a green-colored pigment called chlorophyll which is required to carry out the process of photosynthesis. The chlorophyll pigment absorbs sunlight and uses it to transform carbon dioxide (CO₂) and water (H₂O) into glucose, which will be used up in further processes like respiration.

Plant cell differ from animal cell by the presence of a cell wall outside the cell membrane.

The plant cell is of rectangular shape and is comparatively bigger than the animal cell. Both plant and animal cells are eukaryotic cells and they have few similar cell organelles. When viewed under a microscope we see a plant cell with various components called as cell organelles, which are:

(i) Chloroplast

A chloroplast is a disc shape organelle within a plant cell which allows plants to capture the Sun energy in energy-rich molecules. Both chloroplast and mitochondria evolved from an independent free-living prokaryote, hence they share similar functions.

Chloroplasts are surrounded by two membranes, i.e. bilayered. It is made of phospholipids. The outer membrane is more permeable to small organic molecules, whereas the inner membrane is less permeable and has transport proteins embedded in it. The innermost matrix of chloroplasts is called stroma. It contains metabolic enzymes and multiple copies of the chloroplast genetic material in the form of a circular DNA.

Chloroplasts also have an internal membrane called the thylakoid membrane which contains the light-harvesting complex, including pigments, as well as the electron transport chains which is used in photosynthesis. Each chloroplast contains a green colored pigment called chlorophyll which is required to carry out the process of photosynthesis. The chlorophyll pigment absorbs sunlight and uses it to transform carbon dioxide (CO₂) and water (H₂O) into glucose, which will be used up in further processes like respiration.

(ii) Plasma membrane

Every cell has an outer layer which regulates the inflow and outflow of various substances from a cell which is called a cell membrane. It is also called a plasma membrane. Its main function is to surround and protect the cytoplasm of the cell. Everything from outside has to cross the barrier which is cell membrane only then they can go inside of a cell. The plasma membrane is selectively permeable to ions like hydrogen, calcium, sodium, small molecules like oxygen (O₂), Carbon-dioxide (CO₂) and various larger molecules such as amino acids, glucose, sucrose, etc. Cell membrane performs various functions inside a cell which are osmosis, diffusion, transport of nutrients and molecules into the cell, waste removal, etc. The membrane is made of phospholipids double layer having protein and carbohydrate molecules infused within the lipid bilayer. This fluid-structure provides enough mechanical support and flexibility to allow cells to grow and move.

The Fluid Mosaic Model of the cell membrane was proposed and explained by S.J. Singer and G.L. Nicolson in 1972. The specific proteins present in the double layered membrane are very important for cell-cell recognition and interaction. This interaction allows various cells to acquire oxygen, nutrients, water etc. So basically the cell membrane acts as a gate which keeps the thing outside and inside according to the requirement of the cell.

(iii) Cell wall

Plant cell differ from animal cell by the presence of a cell wall outside the cell membrane. It provides strength, protection against mechanical and osmotic stress to the plant cell and to provide form and structure to the cell. Cell develops turgor pressure against the cell wall. When there is a healthy supply of water, a plant is protected from wilting due to this turgor pressure.

Plant cell walls are made of cellulose, glycoproteins, lignin, pectin, and hemicelluloses. The formation of the cell wall is done by microtubules. It consists of three layers called as primary, secondary and the middle lamella. The primary cell wall is mainly formed by cellulose laid down by various enzymes.

(iv) Lysosomes

Lysosomes are one of the membrane bound organelles which are present in both plant and animal cells. There membrane is also made up of phospholipids. This membrane protects the cell from the hydrolytic enzymes of lysosomes. This organelle inside the plant cell is most important for the process of digestion and excretion. It contains various digestive enzymes which digest the damaged and worn out organelles, bacteria’s, viruses etc. They are also called as “suicidal bags” or “garbage disposable units” of a cell by De Duve.

(v) Chromosomes

Chromosomes are the thread-like entities found in the nucleus of both animal and plant cells. They are made of both protein and nucleic acid, i.e. deoxyribonucleic acid (DNA). These are what makes offspring’s different from their parent while still carrying traits from parents. In humans the parents are two different individuals hence the offspring has the characteristics of both parents, while in plants self fertilization and cross fertilization, both are possible. If we self fertilize a plant, it will be same as its parents because both the parents have the same chromosomes. But if we cross fertilize a plant, then the offspring will be a hybrid having the characteristics of both the plants. Plants have linear chromosomes.

Hence every species of plant have a different set of chromosomes, for example a rice plant has 12 chromosomes while wheat has 42 numbers of chromosomes.

Cells are the smallest entity within a living cell. It is the structural and functional part of all living organisms. So we can say all living like dog, cat, human, horse, insects have multiple cells having multiple specific functions.

So there are two types of cells, unicellular and multi-cellular. And then further its animal cell and plant cell, but all the types of cell have three major functional regions:

(a) Cell Membrane

(b) Nucleus

(c) Cytoplasm

Cell Membrane

Every cell has an outer layer which regulates the inflow and outflow of various substances from a cell which is called a cell membrane. It is also called a plasma membrane. Its main function is to surround and protect the cytoplasm of the cell. Everything from outside has to cross the barrier which is cell membrane only then they can go inside of a cell. The plasma membrane is selectively permeable to ions like hydrogen, calcium, sodium, small molecules like oxygen (O₂), Carbon-dioxide (CO₂) and various larger molecules such as amino acids, glucose, sucrose, etc. Cell membrane performs various functions inside a cell which are osmosis, diffusion, transport of nutrients and molecules into the cell, waste removal, etc. The membrane is made of phospholipids bilayer having protein and carbohydrate molecules infused within the lipid bilayer. This fluid-structure provides enough mechanical support and flexibility to allow cells to grow and move.

The Fluid Mosaic Model of the cell membrane was proposed and explained by S.J. Singer and G.L. Nicolson in 1972. The specific proteins present in the double layered membrane are very important for cell-cell recognition and interaction. This interaction allows various cells to acquire oxygen, nutrients, water etc. So basically the cell membrane acts as a gate which keeps the thing outside and inside when it wants.

Cytoplasm

It is the jelly-like component within the cell which holds everything in its place. It is mostly composed of water along with various nutrients and waste products required by the cell. It provided the enriching environment within the cell for several metabolic reactions to occur systematically.

It serves various functions within the cell:

• It provides mechanical strength to the cell by exerting turgor pressure against the cell's membrane thus maintaining the shape of the cell.

• It is the place for the functioning of most regulatory activities like metabolism, cell division, and protein synthesis within the cell.

• The cytoplasm contains organelles called ribosomes which do protein synthesis.

• It is referred to as the storage house for various small carbohydrate, lipid and protein molecules.

• The cytoplasm can transport and distribute organelles in a discrete manner around the cell.

Nucleus

The nucleus is also called as brain of the cell. It contains the code of life within itself, i.e. DNA (Deoxy-ribonucleic acid) which codes the genetic information of a living entity. It is the largest organelle within the cell. It is present in the eukaryotic cell but is absent in prokaryotic cell, because of which they can be highly distinguished. It has its own covering which separates it from its surrounding cytoplasm called the nuclear envelope. Also, the envelope has certain small pores which regulate the exchange of materials like protein, RNA, etc between the cytoplasm and nucleus. It has chromatin material within the cell consisting of thin long threads of DNA encircled around protein.

Nucleus performs various functions like:

• It controls gene expression and facilitates the replication of DNA during the cell.

• It controls the metabolic reactions within the cell by producing mRNA which codes for enzymes.

• It is the site for protein synthesis, for example, it synthesizes structural proteins like actin which helps in maintaining the shape of the cell.

• It is also the site for ribosomal RNA (rRNA) synthesis, which secretes ribosomes which are important for translation of proteins.

• It is responsible for the transfer of Character from parent to offspring via genetic material (DNA) present inside the nucleus.

(i) There are two main sources of stem cells, the umbilical cord and the bone marrow.

EXPLANATION: Stem cells are special type of human cells which have the potential to develop into various different cell types unlike other cells of human. For example: they can form brain cells from muscle cells or vice versa. These stem cells come from the umbilical cord blood, and hence are called hematopoietic (blood) stem cells. They are specialized to form any type of blood cell like RBCs, WBC and platelets. Because of these humans are able to maintain continuous blood production throughout their lives. These stem cells also arise from bone marrow, which can be called as production house of stem cells. The stem cells reside inside the bone marrow and they released into the bloodstream after they are fully mature. This is from where stem cells come, form blood cells of our whole body and fight against diseases and infections.

(ii) The stem cells can be used in all types of tissues, cells in our body like they can help in forming nervous tissues for patients with neurological disorders, pancreatic cells formation for patients with pancreatic diseases and cardiac muscles formation for patients with heart issues. They can also be used to compensate the loss of blood cells in the human body for example in diseases like thalassemia in which a lot of RBC’s gets destroyed and in leukemia and lymphoma, a lot of WBC’s die losing the ability to protect body thus causing blood cancer. Now a day’s stem cells are also used in transplants for curing stem cells.

EXPLANATION: When a baby is born, the placenta/umbilical cord blood is stored as it is highly rich in stem cells. The stem cells in the spongy part of bone marrow can also be stored for the future cure. These bone marrow and cord blood transplants can provide life to severe life-threatening diseases which are leading to heavy loss of blood cells from the body thus making the immune system highly weak. These stored stem cells can be used to generate new cells in cancer patients whose own cells are damaged or are not functioning. They also help to regenerate damaged tissues and hence may benefit in several disease cure. For example: if a person has cardiac disease, then these stem cells be inserted in the heart muscle so that it can lead to repairing of the defective heart cells.

(iii) According to scientists, there is much more to know about stem cells in the coming future. The research is going on to decipher different capabilities of stem cells in curing diseases. Though there are several challenges in therapies concerning stem cells as sometimes the receiver’s body rejects the transplanted stem cells. Scientists are dealing with similar different challenges to overcome them and build a curable future for mankind.