Cell & Organisms
CELL: A structural and functional unit of all living things is called a cell. These can not be seen by naked eyes.
The shape of the cells:
- Cells are round, spherical or elongated: Red Blood Cells.
- Long and pointed at both ends: have branched like the nerve cell or a neuron.
- Exhibit a spindle shape: Muscle Cells.
Parts of a cell:
- CELL MEMBRANE: Cell Membrane enclosed the other two parts, i.e., cytoplasm and nucleus. It is also called the plasma membrane. Through this, every cell gets separated from the other. It helps to give a shape to a cell.
- CYTOPLASM: Jelly-like substance present between cell membrane and nucleus.
- NUCLEUS: The nucleus is separated from the cytoplasm by a nuclear membrane.
PROKARYOTES: Cells without a well-organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells.
EUKARYOTES: onion cells and cheek cells having a well-organised nucleus with a nuclear membrane are designated as eukaryotic cells.
NUCLEAR MEMBRANE: It is porous and allows the movement of materials between the cytoplasm and the inside of the nucleus.
CELL WALL: It is an outer thick layer of a cell in a plant. Plant cells differ from animal cells in having
an additional layer around the cell membrane termed cell wall.
CHLOROPLAST: Coloured bodies called plastids are found in the plant cells only. Green plastids containing chlorophyll are called chloroplasts.
ORGAN: Organisms are made up of smaller parts called organs and the smallest living part of an organism is called cells.
MULTICELLULAR ORGANISMS: The organisms that are made up of more than one cell are called multicellular organisms. Examples, Plants, Dogs, Insects.
Spirogyra: It is a multicellular organism. Filament presents in it, i.e., the cells are joined end to end to make the thread-like structure.
UNICELLULAR ORGANISMS: Organisms that functions as one cell, are called unicellular organisms.
Examples, Amoeba, Paramecium, Euglena.
- Euglena: It has both plants as well as animal-like characteristics. It has chloroplast. it can move from one place to another by "flagellum", a tail-like structure.
- Amoeba: It can move and can change its shape by “Pseudopodia”.
- Paramecium: It can move by "cilia", a small hair-like structure.
TISSUE: It is a group of similar cells performing a specific function. Each organ is made up of small parts called tissues.
WHITE BLOOD CELL (WBC):
- Can change its shape
Mitochondria: Also called the powerhouse of the cell. Thousands of mitochondria in a cell can depend largely on the function of each cell.
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