Cell: The Building Blocks of Life

Cell - The Building Blocks of Life

• Living organisms consist of cells.
• Cells are typically too small to be seen without a microscope.
• Organisms can be either unicellular (single-celled) or multicellular (many-celled).
• Cells have diverse shapes and sizes.
• Cells contain essential structures that perform specific functions.
• Cells are the structural and functional units of living organisms and carry out all functions to keep the organism alive.
• Cytology is the branch of science focused on studying cells.
• Unicellular organisms include yeast, Amoeba, Chlamydomonas and bacteria.
• Multicellular organisms include fish, birds, trees, insects, and humans.
• Robert Hooke discovered cells by observing tiny "honey-comb like" compartments in a thin slice of cork.

Shape and Size of Cells

• Cells exhibit various shapes, including spherical, oval, rectangular, and cylindrical.
• Most cells are microscopic and require a microscope for viewing.
• Some cells, like a bird's egg, are large enough to be seen with the naked eye.
• The ovum (female reproductive cell) is the largest human cell and can be seen without a microscope, while all other human cells are microscopic.

Activity 1.1: Using a Microscope to Observe Plant and Animal Cells

• Materials needed include a compound microscope, a permanent slide of human RBCs, and a permanent slide of T.S of monocot stem.
• When using the microscope, avoid letting the objective lens touch the glass slide.
• To prepare the slide: Place it on the microscope stage with the specimen over the aperture and clip it in place.
• Adjust the 10X power objective lens, open the diaphragm, and use the eyepiece and mirror to focus light and view the sample.

Activity 1.2: Preparing a Temporary Slide

• Necessary materials include onion, knife/blade, mounting needle, forceps, microscope, glass slide, cover slip, watch glass, water, iodine solution, blotting paper, and dropper.
• Exercise caution when using the knife/blade.
• To prepare a temporary slide: Cut small pieces of the onion bulb, remove a thin peel, place the peel in a watch glass with water, and stain it with iodine.
• The next step is to position the peel on the glass slide using forceps.
• Cover the peel with a cover slip, ensuring no air bubbles are trapped
• Remove excess fluid with blotting paper, and observe under low power.

Internal Cell Structure

• All organisms are composed of cells.
• Cells have specialized parts that include cell membrane, cytoplasm, and nucleus.

Structure of an Animal Cell

• Cell membrane (plasma membrane): The outermost, semi-permeable living layer encloses cell structures and cytoplasm.
• Cytoplasm: A semi-liquid, colorless and translucent substance occupies most of the cell and contains specialized bodies called cell organelles.

Cell Organelles and Their Functions

• Endoplasmic Reticulum: An irregular network connecting the plasma membrane and nuclear membrane.
• Mitochondria: Spherical, oval, or rod-shaped organelles with a double membrane.
• Ribosome: A small organelle scattered in the cytoplasm or attached to the endoplasmic reticulum.
• Golgi Bodies: Small vesicles of different shapes located near the nucleus, consisting of flattened tubes and round structures.
• Centrosome: A star-like structure found only in animal cells, located near the nucleus.
• Vacuoles: Large cavities filled with cell sap, smaller and fewer in animal cells compared to plant cells.
• Nucleus: An oval-shaped organelle in the center of the cytoplasm surrounded by a double-layered nuclear membrane, containing nucleoplasm and nucleoli.

Structure of a Plant Cell

• Plant cells possess all structures found in animal cells, except for the centrosome and have additional structures.
• Cell wall: A rigid, non-living layer made of cellulose that surrounds the cell membrane.
• Plastid: A large organelle surrounded by double membranes.
• Chloroplast: contains chlorophyll (a green pigment) and is found in leaves, stems, and buds.
• Chromoplast: contains various pigments that provide colors to flowers and fruits.
• Leucoplast: a colorless plastid with no pigment, found in endosperm, tubers, and cotyledons.