Cells as basic unit of living organisms - Session 4

Chloroplasts are organelles found in plant cells. They are responsible for photosynthesis. Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose. Chloroplasts are typically oval-shaped organelles with a double membrane. The outer membrane is permeable. A Permeable membrane regulates the exchange of materials between the chloroplast and the cytoplasm of the plant cell.

The inner membrane encloses a semi-fluid matrix called the stroma. Within the stroma, there are membranous sacs called thylakoids. Thylakoids are arranged in stacks called grana. The thylakoids contain a pigment called chlorophyll. Chlorophyll absorbs light energy and converts it into chemical energy. The grana are connected by stromal lamellae, which allow for the exchange of materials between the thylakoids.

Chloroplasts are responsible for capturing energy from sunlight and using it to convert carbon dioxide and water into glucose, through the process of photosynthesis. This glucose is then used by the plant as a source of energy and to build other important molecules.Chloroplasts undertake a crucial role in the survival and growth of plants. Chloroplasts provide energy and nutrients to the plants. Energy and nutrients are necessary for the metabolic processes of plants.

The tonoplast is a type of membrane that is found in plant cells. It is similar in structure to other membranes in the cell, such as the plasma membrane that surrounds the entire cell. Similar to plasma membrane, tonoplast is composed of lipids and proteins, which are arranged in a bilayer.However, the tonoplast is specialized in that it forms a barrier around the central vacuole. Vacuole is a large organelle found in plant cells that stores water, ions and other substances.

The tonoplast allows the movement of ions and other small molecules between the vacuole and the cytoplasm of the cell. The tonoplast can also change its composition in response to different conditions. This allows it to respond to environmental stress and maintain a stable environment for the cell.

The Cell wall is a rigid outer layer that surrounds the cell membrane. It is seen in many types of cells, including bacteria, plants, fungi, and some protists. The cell wall protects the cell from damage and invasion by pathogens such as bacteria and viruses. It also provides structural support to the cell, preventing it from collapsing under its own weight. This is particularly important in plant cells. This is because plants need to maintain their shape to transport water and nutrients.

The structure of the cell wall varies depending on the type of organism. In plants, the cell wall is made up of cellulose fibers. Cellulose fibers are long, thin strands of glucose molecules. These fibers are arranged in a crisscross pattern to form a mesh-like structure. It is then coated with other materials such as lignin, hemicellulose, and pectin. The hemicellulose strengthens the cell wall. Lignin enhances the rigidity of cell wall. It also provides support in transport of minerals. Pectin helps in holding the adjacent cells together.

In bacteria, the cell wall is made up of peptidoglycan. Peptidoglycan is a complex molecule made up of sugar and amino acid chains. It forms a rigid layer that gives the cell its shape and protects it. In bacterial cells, the cell wall controls the flow of molecules across the membrane. It prevents harmful substances from entering the cell and allows beneficial ones to pass through.

We know each plant cell is protected by cell wall. How are materials transported between cells? For this purpose, there are small channels or pores that connect adjacent plant cells. These channel or pores are called Plasmodesmata. They allow for communication and transport of materials between cells. Plasmodesmata are found in all types of plant cells, including the cells of the roots, stems, leaves, and flowers. They are important for plant growth, development and defense against pathogens.

The plasmodesmataconsist of a central channel, called the desmotubule. Desmotubule is surrounded by a membrane lining. The membrane is continuous with the plasma membrane of the two cells that are connected by the plasmodesmata. The desmotubule is thought to be composed of specialized proteins that help maintain the shape and function of the channel. Plasmodesmata can act as a defense mechanism against pathogens. When a plant is infected with a pathogen, neighboring cells can close-off their plasmodesmata to prevent the spread of the pathogen to other parts of the plant.

Microvilli are microscopic, finger-like projections that extend from the surface of some types of cells. They are most commonly found in the lining of the small intestine and kidney tubules. The microvilli consist of a core of actin filaments. Actin filaments are long, thin protein fibers, surrounded by a plasma membrane. The actin filaments are anchored to the cell membrane by a protein complex called the terminal web, which helps to maintain the shape and stability of the microvilli.

Microvilli are particularly important in the small intestine, where they perform a critical role in nutrient absorption. The increased surface area provided by the microvilli allows for more efficient absorption of nutrients from food. The microvilli also contain enzymes that help break-down nutrients, such as carbohydrates and proteins. These nutrients are broken into smaller molecules that can be more easily absorbed by the body.

A virus is a tiny particle that can infect living things, such as plants, animals, and bacteria. Unlike other living organisms, viruses cannot survive or reproduce on their own. They rely on a host cell to survive and reproduce. The structure of a virus consists of genetic material. Genetic material can be DNA or RNA. Genetic material is surrounded by a protective protein coat. This protein coat is called capsid. The primary function of capsid is to protect genetic material of virus.

Some viruses also have an outer envelope made up of lipids that help them enter and exit the host cell. This envelope is surrounded by small projections. These projections are called envelope protein. They help in the interaction between virus and host cell.The main function of a virus is to invade a host cell. After invading, virus takes over the machinery of host cell. It then replicates itself using resources of host cell. This causes various diseases in host.