The Fundamental Unit Of Life

Free- living cells were discovered by Anton Van Leeuwenhoek in the pond water.

(i) unicellular organisms – Amoeba, Paramoecium

(ii) Multicellular organisms- Fungi and Plants

This is a picture showing different unicellular organisms.

i. Amoeba changes its shape through its pseudopodia as it tries to catch its food.

ii. White blood cells in humans change its shape as it engulfs the germs to kill them.

Nerve cell is the longest in human body. It is about one meter long.

This is a diagram showing a nerve cell.

Lipids and proteins contribute to the flexibility of the plasma membrane.

Lipids constitute of 40-80% of the plasma membrane and the remaining is filled with proteins.

The lipids help to give membranes their flexibility and the proteins maintain the cell’s chemical climate and assist in the transfer of molecules across the membrane.

The diagram of plasma membrane is given as:

The plasma membrane separates the contents of the cell from the outer environment. It allows the entry and exit of only selected molecules in and out of the cell, respectively.

Carbon dioxide is removed from the cell through the process of diffusion.

As carbon dioxide is produced, the concentration inside the cell increases to a level higher than the surrounding blood, so carbon dioxide diffuses out of the cell.

Diffusion is a spontaneous movement of a substance from a region of high concentration to a region where its concentration is low.

This is a diagram showing the process of diffusion.

Diffusion also helps in the movement of water across the concentration gradient.

The movement of water molecules from a region of higher concentration to region of lower concentration is known as osmosis, through a semi-permeable membrane.

This is a diagram showing the process of osmosis.

Cell wall is the component of the cell wall that provides the structural strength to it. Cellulose in the cell wall is a complex substance that confers strength to it.

This is a diagram showing the part of the cell wall.

Nuclear pores are protein-based channels in the nuclear envelope

i. The nuclear pores help in the transfer of molecules from inside of the nucleus to the cytoplasm of the cell.

ii. Nuclear pores allow necessary proteins to enter the nucleus from the cytoplasm.

A segment of DNA that is functionally active is known as a gene. They are located in the nucleus of the cell. A gene provides information for the production RNA and then protein, following a series of steps.

Prokaryotes lack the nuclear membrane around the nuclear region in the cell. Nucleic acid of the nucleus is present in an undefined form known as ‘Nucleoid’. That is why, it is said that the nuclear region of the prokaryotes is poorly defined.

This is a diagram showing nucleoid in prokaryotes.

Prokaryotic cells divide by the process of binary fission. The parent cell divides into two daughter cells that are identical to each other. It is a mode of asexual reproduction.

Two prokaryotes are E.coli and streptococcus bacteria.

This is diagram showing the process of binary fission.

Cytoplasm is the fluid content inside the cell membrane. It contains the specialized cell organelles that play important functions in the cell.

The site for protein synthesis in a cell is ribosome.

Protein is needed for many cell functions such as repairing damage or directing chemical processes.

Ribosomes can be found floating within the cytoplasm or attached to the endoplasmic reticulum.

SER stands for Smooth Endoplasmic Reticulum. The role of SER in liver cells of vertebrates is to break down (detoxifying) drugs and poisons.

It is also involved in detoxification, production of biochemicals necessary for digestion and in lipid digestion.

This is a picture showing the Endoplasmic Reticulum.

Endoplasmic reticulum, Golgi apparatus, and lysosomes constitute the complex cellular system in living cells.

During digestion, the lysosomes digest stored food contents by digestive enzymes to supply energy to the cell.

Explanation:

Lysosomes are formed by the Golgi body or the endoplasmic reticulum. These powerful enzymes can digest cell structures and food molecules such as carbohydrates and proteins.

Two similarities between mitochondria and plastids are:

1. They both contain their own DNA content and ribosomes.

2. They both bear the same external structure organization.

The two pictures show the external details of mitochondria and plastid (chloroplast)

Vacuole act as the storage sacs of the cell. It stores cell sap. It maintains the turbidity and rigidity of the cell.

New cells arise from the pre-existing cells. Cells divide and produce new cells of their own kind.

Two examples of organisms in which a single cell performs all the functions are:

1. Amoeba

2. Paramoecium

The cell may die if there are no vacuoles present in the cell. Vacuoles act as the storage sac of the cell for important proteins, vitamins, and amino acids.

The DNA is present in the form of a chromatin material when the cell is not dividing. It is present in an un-winded form.

The DNA molecule contains the necessary information for proper functioning and organization of the cell. It acts as a source of information for the production of RNA and then proteins in the cell.

Chromoplast are present in the coloured part of the plants. It is a type of plastid that imparts colour to the plant parts like flowers, fruits, etc.

The movement of solute particles take place from a region of higher concentration to a region where the concentration of solutes is low. This is diffusion.

Similarly, osmosis involves the movement of water molecules from a region of higher concentration to a region of lower where the concentration of water molecule is low, through a semi-permeable membrane.

This is a picture showing comparison between osmosis and diffusion.

Lysosome is the organelle of the cell which is membrane- bound and contain powerful digestive enzymes,that acts upon harmful pathogens in the cell. It is also known as the suicide bags of the cell.

Membrane bound organelles are found in eukaryotes. Examples – Nucleus and mitochondria.

Organelles in prokaryotes are non- membrane bound. Example- Nucleoid.

Prokaryotic cells lack a nucleus and membrane-bound structures. Eukaryotic cells have a nucleus and membrane-bound structures called organelles

Chemical composition of plant cell wall is cellulosic while that of fungi is made up of chitin.

Plant cell walls are composed of cellulose, while fungi cells walls are composed of chitin.

The shape of the cell depends upon:

1. Function it performs:

They may be spherical, rounded, cuboidal, tubular, discoidal or irregular.

It also depends on the cytoskeleton.

2. Its cytoskeleton

The cytoskeleton supports the cell & gives it shape.

It is responsible for organizing the organelles, and has roles in molecule transport, cell division and cell signaling.

The genetic material of a cell is located in the nucleus. The nucleic acid stores vital information for the proper functioning of the cell.

It is called so because it directs all the important functions that take place in a cell.

This is a diagram showing the nucleus and its internal details.

(i) The organelle observed by Ishita is Rough Endoplasmic Reticulum (RER).

(ii) The rough surface of the organelle is due to the presence of ribsomes on it, which imparts are rough look to it.

(iii) The ribosomes on RER is associated with the manufacturing of proteins in the cell. And, the sending it to the site where they are needed.

(iv) It can be easily observed that Ishita is a keen learner who takes into account every little detail.

Different colours are seen in different fruits and flowers. This is because of the presence of the chromoplast on the cell. Chromoplast is a type of plastid which imparts colour to different parts of the plant.

The nucleus is the most important and efficient organelle among all the other organelles. It stores genetic information in the form of DNA (De-oxyribo nucleic acid). The nucleus plays the most important role in cellular reproduction, the process by which a cell divides to form two daughter cells.

That is why it is said that a cell without a nucleus is without any future, as it will not be able to divide further.

1. FUNCTION OF LEUCOPLAST- They helps in the storage of starch, oils and protein granules in the cell.

2. FUNCTION OF CHROMOPLAST- They impart colour to different parts of the plants like flowers, fruits, etc.

Cytoplasm is the fluid content of the cytoplasm.

Functions- It contain specialized organelles which performs important functions in the cell.

Eukaryotic nucleus

Diagram showing eukaryotic nucleus

It is different from nucleoid of prokaryotes as, eukaryotic nucleus contains well-defined nuclear membranes but in prokaryotes the nuclear membrane is absent. The genetic content is present as nucleoid.

Diagram showing nucleoid in prokayotic bacteria.

(i) A- chloroplast

B-vacuole

C- ribosome

D- cytoplasm

E-nuclear membrane

F-nucleus

G- tonoplast

H- cell wall

(ii) It is a plant cell as it shows cell wall. Animal cell do not contains cell wall.

(iii) Functions:

1. A (chloroplast) – It helps in carrying out the process of photosynthesis in plants.

2. F (Nucleus) - It contains all the genetic information in the form of DNA.

3. H (cell wall) – It is made up of cell wall. Provides strength to the cell.

(i) It degrades the soil fertility. As excess of salt will make the soil hypertonic, due to which the water from roots will move out through osmosis. And, as a result the crop will die.

(ii) It is based upon on the concept of osmosis. Salt enter the cell and water will eventually move out of the cell to maintain the osmotic level. This prevents the mango from rotting.

Osmosis- It is the movement of water molecules from a region of high concentration to a region of low concentration. Swollen feet gets cured when soaked in salt water as it reduces inflammation in the muscles. And, salt particles move inside the feet through the membrane in order to maintain solute – solvent level. These salt particles give relief to the feet muscles.

Diffusion is the movement of solute particles only. Plasmolysis is the movement of water when placed in a hypertonic solution while de-plasmolysis is the movement of water hypotonic solution.

Because ribosome help in the production of protein molecules and enzymes for the cell to work efficiently.

But hormone and starch molecule formation is not carried out by ribosomes.

This is because it imparts colour to different parts of the plant. Chromoplast that contain chlorophyll pigment is chloroplast.

Amylopast is responsible for the synthesis of starch granules whole leucoplast serves the function of storing it.

Ovum is responsible for the production of new cells through the process of fertilization. Fat cells (b) stores fat. (c) bone cell is present in the bones and (d) muscle cell is present in the muscles.

Because, Golgi apparatus performs the function packaging, storage and modification of products in vesicles.

Cytoplasmic bridges are known as plasmodesmata.

Because, other than ribosomes all other organelles are found in eukaryotes only.

Deoxyribonucleic acid

Because, cell wall of plants is made up of cellulose and pectins.

Are small-sized in animal cell and large-sized in plant cell. In plant cell they are located centrally and cover about 90% of space.