The Fundamental Unit Of Life

Viruses are considered as an intermediate between living and non-living cells because they cannot metabolite* and reproduce on their own. They can reproduce only when enters in a host's body. They are an exception to cell theory. Viruses can be easily made into crystal.

*Metabolite: Metabolites are the products of metabolism.

If a cell placed in the hypotonic solution, then it will be swell up. This is because the higher concentration of water molecules is present outside the cell. So, the water molecules move from external solution into cell sap.

Chromosomes are thread like structures usually present in the nucleus. They are composed of DNA (deoxyribose nucleic acid) and proteins.

Ribosomes are small and dense particles which occur freely in the cytosol or remain attached to the endoplasmic reticulum. They take part in the synthesis of proteins. It also helps in manufacture of enzymes

Endoplasmic reticulum serves as channels and helps in transporting the different materials like proteins between various regions in the cytoplasm as well as between the nucleus and the cytoplasm. It also provides a large surface area inside the cells for various chemical activities.

Osmosis is a movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane.

Plasmolysis is defined as the process of shrinkage of the cytoplasm of a plant cell occurred due to loss of water in the plant cell.

Vacuoles are fluid-filled membrane-bound spaces. They are bounded by a single unit membrane known as tonoplast.

The part of the cell which occur between the cell membrane and nucleus envelope is called cytoplasm. Cytoplasm contains many specialised cell organelles. While protoplasm consists of cytoplasm and nucleus.
Basically : Protoplasm = Cytoplasm + Nucleus

Lysosomes are tiny sac-like structures found in the cytoplasm. Each lysosome is surrounded by a single membrane and contains powerful enzymes. These enzymes are made by rough endoplasmic reticulum.

Smooth endoplasmic reticulum (SER) does not bear ribosomes. It plays a crucial role in detoxifying many poisons and drugs.

Smooth endoplasmic reticulum does not bear ribosome. It helps in the synthesis of lipids While, rough endoplasmic reticulum is associated with ribosomes. Ribosomes are site of protein synthesis.

A Prokaryotic cell is primitive in organisation. It has a nucleoid (nuclear membrane is absent).

The cell organelle involved in forming complex sugars from simple sugars are Golgi apparatus.

Vacuole performs following functions in plant cells:

(i) Vacuole helps in osmoregulation in a cell.

(ii) It stores toxic metabolic by-products or end products of the plant cell.

(iii) It helps in maintaining turgidity of the cell.

Endocytosis is the ingestion of material by the cells through the plasma membrane. Amoeba acquires its food through endocytosis process.

Bacterial cell wall is made up of peptidoglycan. The other name for peptidoglycan is murein. It is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane, which forms the cell wall in bacteria cell.

Silver nitrate solution is used to study Golgi apparatus.

Nucleus, mitochondria and plastid have their own DNA, hence they are able to make their own structural proteins.

Chloroplast is known as kitchen of the cell as photosynthesis takes place in them.

Smooth endoplasmic reticulum (SER) does not bear ribosomes. They are found in liver cells, interstitial cells, adipose cells and muscles cells, etc. They help in the manufacture of fat molecules and lipids.

Rudolf Virchow (1858) stated that the new cells originate from the pre-existing cells only (omnis cellula e cellula).

Two biologists, Schleiden (1839) and Schwann (1839) presented the cell theory. This stated that all the plants and animals are composed of cells and the cell is the basic unit of life.

Ribosomes are present both in prokaryotic and eukaryotic cells except in Matura sperms and RBCs. They are made up of ribonucleic acid (RNA) and proteins.

Ribosomes are small and dense particles which occur freely in the cytosol or remain attached to the endoplasmic reticulum. They take part in the synthesis of proteins. Ribosomes are not bounded by a membrane.

1 μ m (1 micro-meter) is 10^–6 m. Also

1mm (1 milli-meter) = 10^–3 m

1 nm (1 nano-meter) = 10^–9 m

The main function of Golgi apparatus is secretion, packaging and modifying of the proteins. It is also involved in the synthesis of new membrane and lysosomes.

First living cells were observed by A.V. Leeuwenhoek. These were single- celled micro-organisms called prokaryotes.

Plasma membrane is selective permeable membrane made up of lipids and proteins. The movement of water across a semipermeable membrane is affected by the amount of substances dissolved in it.

Lysosomes are membrane-bound organelles that contain powerful digestive enzymes. They digest excess or worn out organelles, food particles and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Sometimes, lysosomes can cause self-destruction of a cell by releasing these digestive enzymes within the cells, hence they are also known as suicide bags. .

Yes, All living organisms are made up of cells. Cell are building block of life. In unicellular organisms, a single cell performs all basic functions of life. While in multicellular organisms, Cells become specialised to perform different functions. Similar cells group together to form tissue for e.g. muscular tissue. Tissues organised to form organs such as heart, kidney and then organ organise into organ system (Circulatory system, excretory system, digestive system, etc.) to perform major functions. A living organism has a number of organ systems. Thus, in all such organisational complexity, cell remains the basic building unit of the organism.

Soap and detergent solutions are used to wash clothes which are hypertonic* in nature as compared to the skin cells. This results in exosmosis in the skin cells and thus the skin over the fingers shrinks when we wash clothes for a long time.
*Hypertonic solutions: In hypertonic solutions, the concentrations of dissolved solutes are greater outside the cell resulting in the low concentration of water outside. Thus, to maintain an equilibrium, the water will flow from inside to the outside, causing the cell to shrink.

The process by which cells engulf food is called endocytosis. The flexibility of plasma membrane helps the cell to engulf in food and other substances from its external environment. This is possible only when plasma membrane is in direct contact with external medium which happens only in the case of animals. In the case of plants, plasma membrane is covered with a wall, as you can see in the image itself:

Concentrated salt solution is a hypertonic solution which causes dehydration in the alimentary canal* due to exosmosis*. This causes stretching and hence vomiting.

*Exosmosis: The passage of a fluid through a semipermeable membrane from high concentration solution to a lower concentration.
*Alimentary canal: The whole passage through which the food passes through the body from the mouth to the anus.

Ribosomes are not bounded by a membrane. Ribosomes are responsible for translating the DNA code to actual proteins which is used by the cells for other purposes and functioning.
They are unique as they are not bounded by any membranes. It is so because it allows them to easily pick up translational RNA (ribo-nucleic acid) which is released from the nucleus.

Digested food is absorbed in the intestinal cells by the following process:

(i) Glucose and amino acids -Active transport.

(ii) Fatty acids and glycerol – Diffusion (Passive transport)

(iii) Water – Osmosis.
The digestion process is shown below:
Digestion Diagram

On adding salt in the vegetables, then the concentration in the outer medium increases than the inside medium. This makes the external medium hypertonic because of which exosmosis occurs and vegetables release water.
*Hypertonic solutions: In hypertonic solutions, the concentrations of dissolved solutes are greater outside the cell resulting in the low concentration of water outside. Thus, to maintain an equilibrium, the water will flow from inside to the outside, causing the cell to shrink.

(b) RBC will burst easily while cells of onion peel will resist the bursting to some extent because RBC doesn’t have mechanism to resist endosmosis while onion cell wall puts a mechanical barrier to promote entry of water.

Photoautotrophs are those which carry out the process of photosynthesis. Though bacteria do not contain any chloroplast but they do certain pigments contain photosynthetic pigments inside small vesicles. Due to these they are able to perform photosynthesis.

(a) : iv

(b) : v

(c) : iii

(d) : i

(e) ii.

1. Chromoplast : Flower (petals) and fruits.
Chromoplasts are coloured plastids other than chloroplasts. Plastids are a class of small organelles.

2. Chloroplast : Green leaves and green stem.
Chloroplasts are the plastids that contain chlorophyll and the process of photosynthesis takes place in it.

3. Leucoplast : Root and underground stem.
Leucoplast is a colourless organelle found in plant cells, used for the storage of starch.

(a) Endoplasmic reticulum

(b) Mitochondria

(c) Golgi apparatus

(d) Lysosome

(e) Vacuole

(f) Chloroplasts

(g) Nucleus.

Diffusion is the process in which particles move from a region where they are in higher concentration to a region where they are in low concentration, until uniform concentration is finally achieved. Carbon dioxide (CO₂) moves in and out of the cells by the process of diffusion.

Osmosis is a special type of diffusion. Osmosis is diffusion of water from the region of its higher concentration (pure water or dilute solution) to the region of its lower concentration (strong solution) though a semipermeable membrane. Water moves in and out of the cells by osmosis.

Both diffusion and osmosis are physical or mechanical processes and do not require spending of energy for their performance by the cells.

Amoeba obtain its food through the process of endocytosis. The plasma membrane of Amoeba is flexible which help to engulf its food particles and other material from its external environment.

There are certain organelles that have their own genetic material. Example: Mitochondria and plastids are two cell organelles that contain their own genetic material.
Mitochondria is called the power house of the cell. The main function of Mitochondria is the production of the energy in the form of ATP i.e. Adenosine triphosphate.

Lysosomes are called scavengers of the cell because they remove cell debris consisting of dead and worn out cell organelle by digesting the same. They help in cleaning the dead and the worn-out cells. In this way, they maintain the cellular metabolism.

Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell. The two main functions of the nucleus of the cell are:
i) It stores the genetic material (also called as the DNA of the cell)
ii) It coordinates the cell activities such as growth, metabolism, protein synthesis and the reproduction functions.

(a) Leucoplasts in roots
Leucoplast is a colourless organelle found in plant cells, used for the storage of starch.

(b) Chloroplasts in leaves
Chromoplasts are coloured plastids other than chloroplasts. Plastids are a class of small organelles.

(c) Chromoplasts in flowers and fruits.
Chloroplasts are the plastids that contain chlorophyll and the process of photosynthesis takes place in it.

Plant cells possess large sized vacuole because it performs following functions in plant cells:

(i) Vacuole helps in osmoregulation in a cell.

(ii) It stores toxic metabolic by-products or end products of the plant cell.

(iii) It helps in maintaining turgidity of the cell.

The following image shows the vacuoles inside the cell.

Chromatin is a tangled fibrous mass made up of DNA and protein. The chromatin material condenses to form chromosomes during cell division. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes. A chromosome consists of two identical and spirally coiled threads called sister chromatids. They are joined at a constriction called centromere.
The following picture shows the chromatin, chromatid and chromosome in the cell.

(a) A cell having higher water content than the surrounding medium, meaning that the surrounding solution is very concentrated solution (hypertonic solution), the cell will lose water by exosmosis. Such a solution is known as hypertonic solution.
*Hypertonic solutions: In hypertonic solutions, the concentrations of dissolved solutes are greater outside the cell resulting in the low concentration of water outside. Thus, to maintain an equilibrium, the water will flow from inside to the outside, causing the cell to shrink.

(b) A cell having low water concentration than the surrounding medium, meaning that the surrounding solution is very dilute (hypotonic solution), the cell will gain water by endosmosis. Such a solution is known as hypotonic solution.

(c) A cell having equal water concentration to its surrounding medium, the cell will neither gain nor lose water to the external medium. Such a solution is known as isotonic solution.

The plant cell is shown below:

(a) Nucleus: It determines the function and development of the cell

(b) Golgi apparatus: It packages materials coming from the endoplasmic reticulum

(c) Cell wall: It provides resistance to microbes to withstand hypotonic external media without bursting

(d) Cytoplasm: It is a is site for many biochemical reactions necessary to sustain life.

(e) Nucleoplasm: It is a fluid contained inside the nucleus

The following diagram gives the complete description of a plant cell.

Differences between plant and animal cells:

A neatly labelled diagram of an animal cell is shown below:

Differences between nucleus and nucleoid:

The following diagram give the structure of Smooth and Rough endoplasmic reticulum.

Plasma membrane is made up of lipid and proteins. Endoplasmic reticulum is of two types-

(i) Rough endoplasmic reticulum with ribosomes attached on its surface for synthesizing proteins.

(ii) Smooth endoplasmic reticulum which is without ribosomes and is engaged in the synthesis of lipids.

Thus, endoplasmic reticulum acts as main site for synthesis of proteins and lipids which are needed for biosynthesis of plasma membrane. Hence, it is important for membrane biosynthesis.

(a) When dry apricot is placed in pure water, it gains water and swells due to endosmosis. After that if the swollen apricot is placed in the concentrated sugar solution, it loses water and consequently shrinks again due to exosmosis.

(b) When red blood cells are placed in concentrated salt solution, the water molecule will come out and it will shrink and give a shrivelled appearance (crenation).

(c) Breakdown of plasma membrane will result in death of the cell as protoplasmic structures will get dispersed.

(d) When Rheo leaves are boiled, all the cells of leaves become dead. When sugar solution is added on to the boiled rheo leaves, nothing will happen because liquid cannot pass through dead cell membrane.

(e) If Golgi apparatus is removed from the cell, the most cell activities performed by the Golgi apparatus will not take place.

The following diagram is of plant cell and the main parts which makes a plant cell different from animal cell are:

1) Chloroplast: Chloroplast are contains chlorophyll and the process of photosynthesis takes inside them.

2) Vacuole: Vacuole is a space inside the cytoplasm of a cell which contains fluid. It is enclosed by a membrane.

3) Cell Wall: The outermost layer of cells in plants, bacteria, fungi, and many algae that gives shape to the cell and protects it from infection is called as cell wall. It is made up mostly of cellulose.