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Questions and Answers
Who discovered cells, and in what year?
Robert Hooke discovered cells in 1665.
Explain why the cell is called the structural and functional unit of life.
The cell is called the structural and functional unit of life because it is the basic building block of all living organisms and performs essential functions required for life.
What is the Structural Organisation of a Cell?
The structural organization of a cell involves the arrangement of organelles within the cell.
What is the role of diffusion in a cell?
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What is the net diffusion of water across a selectively permeable membrane known as? Osmosis is the net diffusion of water across a selectively permeable membrane toward a higher _______ concentration.
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Animal cells can withstand very dilute external media without bursting due to their cell walls.
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Match the following organelles with their function: 1. Chloroplasts, 2. Nucleus, 3. Ribosomes
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Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Size: generally small (1-10 µm) Eukaryotic Cell: Size: generally ____ (5-100 µm)
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Prokaryotic Cell: Chromosome: single Eukaryotic Cell: Chromosome: more than one ________
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What is the function of lysosomes in a cell?
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Which cell organelle plays a crucial role in detoxifying poisons and drugs in liver cells of vertebrates?
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Match the cell organelles with their functions:
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Can you name the two organelles we have studied that contain their own genetic material?
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Why are lysosomes known as suicide bags?
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Where are proteins synthesized inside the cell?
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What is the energy currency of the cell?
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Why do plant cells have very large vacuoles?
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Can you think as to why the chromosome number has reduced to half in daughter cells during meiosis?
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Study Notes
The Fundamental Unit of Life
- The cell is the basic unit of life, discovered by Robert Hooke in 1665.
- Hooke observed the cells in a cork slice with the help of a primitive microscope.
- Later, Antonie van Leeuwenhoek (1674) discovered free-living cells in pond water, and Robert Brown (1831) discovered the nucleus in a cell.
What are Living Organisms Made Up Of?
- All living organisms are made up of cells, which are the basic building units of life.
- Robert Hooke coined the term "cell" to describe these units, and it is still used today in biology.
- Cells can be observed under a microscope, and they are the structural and functional units of life.
Characteristics of Cells
- Cells are the basic units of life, and all living organisms are made up of one or more cells.
- Cells can be single-celled (unicellular) or multi-celled (multicellular) organisms.
- Unicellular organisms, such as Amoeba, Chlamydomonas, and bacteria, are capable of performing all basic functions of life.
- Multicellular organisms, such as plants and animals, have different cells performing different functions.
Cell Structure and Organisation
- A cell has three main features: plasma membrane, nucleus, and cytoplasm.
- The plasma membrane is the outermost covering of the cell, which separates the cell's contents from its external environment.
- The nucleus is the control center of the cell, where genetic information is stored.
- Cytoplasm is the fluid substance inside the cell, where various cell organelles perform specific functions.
Cell Organelles and Functions
- Each cell organelle performs a specific function, such as making new material, clearing waste, and regulating cell activities.
- All cells, regardless of their function or organism, have the same basic organelles.
- Cell organelles work together to constitute the basic unit of life, the cell.
Cell Membrane and Transport
- The plasma membrane is selectively permeable, allowing certain substances to enter or leave the cell.
- Diffusion is the process of movement of substances from a region of high concentration to a region of low concentration.
- Osmosis is a special case of diffusion, where water molecules move across a selectively permeable membrane.
- Cells can gain or lose water through osmosis, depending on the concentration of the surrounding solution.
Cell Wall and Nucleus
- Plant cells have an additional rigid outer covering called the cell wall, which lies outside the plasma membrane.
- The cell wall is mainly composed of cellulose and provides structural strength to plants.
- The nucleus is the control center of the cell, where genetic information is stored.### Cellular Structure and Functions
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Cellular Structure:
- Cells have a cell wall, plasma membrane, cytoplasm, and nucleus.
- Prokaryotic cells lack a nuclear membrane and membrane-bound organelles, while eukaryotic cells have these features.
Plasmolysis
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Plasmolysis:
- Occurs when a living plant cell loses water through osmosis, causing the cell contents to contract away from the cell wall.
- Can be observed by mounting a Rhoeo leaf in a sugar or salt solution and observing under a microscope.
Cell Organelles
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Nucleus:
- Contains chromosomes, which are visible as rod-shaped structures only during cell division.
- Chromosomes contain DNA molecules, which have the information necessary for constructing and organizing cells.
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Endoplasmic Reticulum (ER):
- A large network of membrane-bound tubes and sheets.
- Divided into two types: Rough Endoplasmic Reticulum (RER) with ribosomes attached and Smooth Endoplasmic Reticulum (SER) involved in lipid synthesis.
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Golgi Apparatus:
- A system of membrane-bound vesicles that modify, package, and dispatch products synthesized near the ER.
- Consists of a complex cellular membrane system.
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Lysosomes:
- Membrane-bound sacs filled with digestive enzymes that break down foreign materials, worn-out organelles, and cellular waste.
- Known as the "suicide bags" of the cell, as they can break down the cell itself if needed.
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Mitochondria:
- Known as the "powerhouses" of the cell, generating energy for the cell through ATP production.
- Have their own DNA and ribosomes, allowing them to make some of their own proteins.
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Plastids:
- Present only in plant cells, with two types: chromoplasts (colored) and leucoplasts (white or colorless).
- Chloroplasts contain chlorophyll and are responsible for photosynthesis.
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Vacuoles:
- Membrane-bound sacs that store cell sap, providing turgidity and rigidity to plant cells.
- Involved in storage and digestion of cellular waste and foreign materials.
Cell Division
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Cell Division:
- The process by which new cells are made, allowing organisms to grow, replace old cells, and form gametes for reproduction.### Cell Structure
- The cell membrane is an active part of the cell, regulating the movement of materials between the cell and its environment.
- In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane, allowing cells to exist in hypotonic media without bursting.
- The nucleus in eukaryotes is separated from the cytoplasm by a double-layered membrane and directs the life processes of the cell.
Organelles
- The ER functions as a passageway for intracellular transport and as a manufacturing surface.
- The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification, and packaging of substances manufactured in the cell.
- Plastids are membranous organelles found in plant cells, of which there are two types: chromoplasts and leucoplasts.
- Chromoplasts contain chlorophyll and perform photosynthesis, while leucoplasts perform storage functions.
Vacuoles
- Vacuoles are storage sacs for solid or liquid contents.
- Plant cells have very large vacuoles, while animal cells have small-sized vacuoles.
- The central vacuole of some plant cells can occupy 50-90% of the cell volume.
Cell Division
- There are two main types of cell division: mitosis and meiosis.
- Mitosis is the process of cell division that results in two identical daughter cells, each with the same number of chromosomes as the mother cell.
- Meiosis is a process of cell division that involves two consecutive divisions, resulting in four new cells with half the number of chromosomes as the mother cell.
Cell Types
- Prokaryotic cells have no membrane-bound organelles, and their chromosomes are composed of only nucleic acid.
- Eukaryotic cells have membrane-bound organelles and chromosomes composed of nucleic acid and proteins.
Cell Functions
- Cells in organisms divide for growth of body, replacement of dead cells, and formation of gametes for reproduction.
- Cells can obtain food through various means, such as osmosis.
- Osmosis is the movement of water molecules from a high concentration to a low concentration through a selectively permeable membrane.
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Description
This quiz is about the discovery of cells and the structure of a honeycomb-like pattern found in cork. It covers the basics of cell biology and the tools used to observe cells.
