Function of Organelles in Cells
Animal and Plant cells have features in common
Though plants and animals cells are very different they also have many things in common. In both of these, the cells are surrounded by a very, thin plasma membrane. Each cell also contains a nucleus, chromatin, and DNA, which is in the chromatin. Within the nucleus is the nucleolus which is made of loops of DNA from several chromosomes.The material between the nucleus and the plasma membrane is known as the cytoplasm. in the cytoplasm there are many small organs known as organelles.
Differences between plant and animal cells
The only structure that is absent in from a plant cell that is commonly found in an animal cell is the centriole. under a light microscope, this structure appears close to the nucleus and is involved in nuclear division. There are several structures not seen in an animal cell that are seen in a plant cell. A plant cell contains a cell wall, which is located outside of the plasma membrane.The cell wall gives the cell definite shape, prevents it from bursting when osmosis occurs, and gives the cell extra strength. Mature plant cells have a large central vacuole and, if the cell carries out photosynthesis, in containing chloroplasts.The vacuole is surrounded by a membrane,the tonoplast, which controls exchange between the vacuole and the cytoplasm.
Structure and function of organelles
Nucleus
The nucleus is the largest cell organelle. It is surrounded by two membranes known as the nuclear envelope.The nuclear envelope is perforated by nuclear pores. These allow exchange between the nucleus and the cytoplasm. Within the nucleus, the chromosomes are in a loosely coiled state called chromatin. Chromosomes contain DNA which is organized into functional units called genes. Genes control the activities of the cell and inheritance. Therefore the nucleus controls the cells activities
Centrioles
Centrioles appear right outside the nucleus. They lie close together at right angles to each other. A centriole is a hollow cylinder formed by a ring of mircotubules. These are used to grow spindle fibers for nuclear division.
Endoplasmic Reticulum (ER) and Ribosomes
An extensive system of membranes running through the cytoplasm is known as the endoplasmic reticulum. Attached to the surface of the ER are many tin organelles known as ribosomes. ER that lacks ribosomes is known as smooth ER and is now known to have a different function that rough ER, which has ribosomes. The membranes form a flattened system of sacs called cisternae. The cisternae go on to for the Golgi apparatus. Ribosomes are the sites of protein synthesis. They are found free in the cytoplasm and on the rough ER. They are small organelles made of RNA and proteins.
Golgi Apparatus
The Golgi apparatus is a stack of flattened sacks. the stack is constantly being formed at one end from vesicles which bud ff from the ER, and broken down again at other end to form Golgi vesicles. The apparatus collects, processes, and sorts molecules. Golgi vesicles are also used to make lysosomes.
Lysosomes
Lysosomes are spherical sacs, surrounded by a single membrane and having no internal structure. they contain hydrolytic enzymes which must be kept separate from the rest of the cell to prevent damage. Lysosomes are responsible for the breakdown of unwanted structures.
Mitochondria
Mitochondria are slightly larger than lysosomes and are surrounded by two membranes. The inner part of mitochondria is folded to form finger like cisternae which project into the interior solution. The main function of the mitochondria is to carry out the later stages of aerobic respiration.
Plasma Membrane
The plasma membrane is extremely thin. At high magnifications, it three layers are visible. This consists of two dark lines on either side of a a narrow, pale interior. The membrane is partially permeable, controlling exchange between the cell and its environment.
Cilia
Some have long, thin extensions that can move in a wave like manner. If there are just a few of the extensions, and they are relatively long, they are called flagella. If there are many of them, and they are short, they are called cilia. It is covered with an extension of plasma membrane and it contains mircotubules that extend throughout length. The movement of cilia and flagella is caused by the mircotubules, which slide against each other, causing the whole structure to bend.
The nucleus is the largest cell organelle. It is surrounded by two membranes known as the nuclear envelope.The nuclear envelope is perforated by nuclear pores. These allow exchange between the nucleus and the cytoplasm. Within the nucleus, the chromosomes are in a loosely coiled state called chromatin. Chromosomes contain DNA which is organized into functional units called genes. Genes control the activities of the cell and inheritance. Therefore the nucleus controls the cells activities
Centrioles
Centrioles appear right outside the nucleus. They lie close together at right angles to each other. A centriole is a hollow cylinder formed by a ring of mircotubules. These are used to grow spindle fibers for nuclear division.
Endoplasmic Reticulum (ER) and Ribosomes
An extensive system of membranes running through the cytoplasm is known as the endoplasmic reticulum. Attached to the surface of the ER are many tin organelles known as ribosomes. ER that lacks ribosomes is known as smooth ER and is now known to have a different function that rough ER, which has ribosomes. The membranes form a flattened system of sacs called cisternae. The cisternae go on to for the Golgi apparatus. Ribosomes are the sites of protein synthesis. They are found free in the cytoplasm and on the rough ER. They are small organelles made of RNA and proteins.
Golgi Apparatus
The Golgi apparatus is a stack of flattened sacks. the stack is constantly being formed at one end from vesicles which bud ff from the ER, and broken down again at other end to form Golgi vesicles. The apparatus collects, processes, and sorts molecules. Golgi vesicles are also used to make lysosomes.
Lysosomes
Lysosomes are spherical sacs, surrounded by a single membrane and having no internal structure. they contain hydrolytic enzymes which must be kept separate from the rest of the cell to prevent damage. Lysosomes are responsible for the breakdown of unwanted structures.
Mitochondria
Mitochondria are slightly larger than lysosomes and are surrounded by two membranes. The inner part of mitochondria is folded to form finger like cisternae which project into the interior solution. The main function of the mitochondria is to carry out the later stages of aerobic respiration.
Plasma Membrane
The plasma membrane is extremely thin. At high magnifications, it three layers are visible. This consists of two dark lines on either side of a a narrow, pale interior. The membrane is partially permeable, controlling exchange between the cell and its environment.
Cilia
Some have long, thin extensions that can move in a wave like manner. If there are just a few of the extensions, and they are relatively long, they are called flagella. If there are many of them, and they are short, they are called cilia. It is covered with an extension of plasma membrane and it contains mircotubules that extend throughout length. The movement of cilia and flagella is caused by the mircotubules, which slide against each other, causing the whole structure to bend.
Chapter 1 Summary
- All organisms are composed of units called cells
- All cells are surrounded by a partially permeable membrane that controls exchange between the cell and its environment
- The cells of animals and plants are compartmentalized and contain many similar structures: plasma membrane; cytoplasm containing mitochondria, ER, lysosomes, and ribosomes; and a nucleus with a nucleolus and chromatin
- Animal cells also have Centrioles and sometimes cilia, whereas most plant cells have chloroplasts and a large central vacuole. Plant cells are also surrounded by rigid cell walls.
- Greater detail and smaller structures are seen with electron microscopes which use electron beams transmitted through or bounced off the specimen However, only dead material can be viewed in electron microscopes.
- Prokaryote cells differ from eurkaryote cells in being smaller, having free DNA in the cytoplasm, no ER or nucleus, few organelles and smaller ribosomes.
- In multicellular organisms, cells are organized into groups called tissues. Groups of different tissues make organs.