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Questions and Answers
Who discovered cells, and how?
Who discovered cells, and how?
Robert Hooke discovered cells in 1665 by observing them in a cork slice under a primitive microscope.
Why is the cell called the structural and functional unit of life?
Why is the cell 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. Cells perform essential functions and are the smallest unit that exhibits the characteristics of life.
Can you name the two organelles we have studied that contain their own genetic material?
Can you name the two organelles we have studied that contain their own genetic material?
Mitochondria and plastids
Why are lysosomes known as suicide bags?
Why are lysosomes known as suicide bags?
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Where are proteins synthesized inside the cell?
Where are proteins synthesized inside the cell?
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Can you think as to why the chromosome number has reduced to half in daughter cells during meiosis?
Can you think as to why the chromosome number has reduced to half in daughter cells during meiosis?
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Which organelle is known as the powerhouse of the cell and why?
Which organelle is known as the powerhouse of the cell and why?
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Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Size: generally ______ (1-10 µm), Chromosome: single, Membrane-bound cell organelles ______. Eukaryotic Cell: Size: generally ______ (5-100 µm), Chromosome: More than one chromosome, Membrane-bound cell organelles ______.
Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Size: generally ______ (1-10 µm), Chromosome: single, Membrane-bound cell organelles ______. Eukaryotic Cell: Size: generally ______ (5-100 µm), Chromosome: More than one chromosome, Membrane-bound cell organelles ______.
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What is the structural organization of a cell?
What is the structural organization of a cell?
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What happens when an animal cell or a plant cell is placed into a solution of sugar or salt?
What happens when an animal cell or a plant cell is placed into a solution of sugar or salt?
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The movement of water across the plasma membrane is also affected by the amount of substance dissolved in water. This net diffusion of water across a selectively permeable membrane is called ____________.
The movement of water across the plasma membrane is also affected by the amount of substance dissolved in water. This net diffusion of water across a selectively permeable membrane is called ____________.
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The plasma membrane is made up of organic molecules called lipids and carbohydrates.
The plasma membrane is made up of organic molecules called lipids and carbohydrates.
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Match the following cell structures with their descriptions:
Match the following cell structures with their descriptions:
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What is found inside the nucleus of a cell?
What is found inside the nucleus of a cell?
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Fill in the gaps in the table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Size: generally small (1-10 µm) Eukaryotic Cell: Size: generally __________ (5-100 µm)
Fill in the gaps in the 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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Fill in the gaps in the table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Chromosome: single Eukaryotic Cell: Chromosome: ____________
Fill in the gaps in the table illustrating differences between prokaryotic and eukaryotic cells: Prokaryotic Cell: Chromosome: single Eukaryotic Cell: Chromosome: ____________
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What is the function of lysosomes in a cell?
What is the function of lysosomes in a cell?
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Which organelle is involved in the detoxification of poisons and drugs in liver cells?
Which organelle is involved in the detoxification of poisons and drugs in liver cells?
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Study Notes
The Fundamental Unit of Life
- In 1665, Robert Hooke discovered cells while examining a thin slice of cork with a self-designed microscope.
- Hooke called these units "cells," a Latin word for "a little room," which is still used today in biology.
- The discovery of cells marked a significant milestone in the history of science, revealing that living things are composed of separate units.
What Are Living Organisms Made Of?
- All living organisms are made up of cells.
- Cells are the basic building units of life.
- Even single-celled organisms like Amoeba, Chlamydomonas, Paramoecium, and bacteria are made up of cells.
- Multicellular organisms, such as plants and animals, are composed of many cells that group together to form various body parts.
What Is a Cell Made Up Of?
- A cell has three main features: plasma membrane, nucleus, and cytoplasm.
- The plasma membrane is the outermost covering of the cell, separating its contents from its external environment.
- The plasma membrane is selectively permeable, allowing or permitting the entry and exit of certain materials into and out of the cell.
Plasma Membrane
- The plasma membrane is flexible and made up of organic molecules called lipids and proteins.
- The flexibility of the plasma membrane enables the cell to engulf food and other material from its external environment through a process called endocytosis.
- The plasma membrane is also responsible for gaseous exchange between the cell and its external environment.
Osmosis
- Osmosis is the net diffusion of water across a selectively permeable membrane toward a higher solute concentration.
- If a cell is placed in a hypotonic solution (lower concentration of water), it will gain water by osmosis and swell.
- If a cell is placed in an isotonic solution (same concentration of water), there will be no net movement of water across the cell membrane.
- If a cell is placed in a hypertonic solution (higher concentration of water), it will lose water by osmosis and shrink.
Cell Wall
- Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall.
- The cell wall is composed mainly of cellulose, a complex substance that provides structural strength to plants.
- The cell wall allows plant cells to withstand very dilute external media without bursting.
Nucleus
- The nucleus is another important organelle of the cell.
- The nucleus was discovered by Robert Brown in 1831.
- The nucleus is an essential organelle found in all living cells.
Cell Organelles
- Each cell organelle performs a special function, such as making new material in the cell, clearing waste material from the cell, and so on.
- All cells have the same organelles, regardless of their function or the organism they are found in.
- The cell organelles together constitute the basic unit of life called the cell.### Cell Structure and Function
- Living plant cells lose water through osmosis, causing contraction of the cell contents away from the cell wall, known as plasmolysis.
- The nucleus is a double-layered membrane structure containing chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
- Chromosomes contain DNA molecules, which carry genetic information for inheritance of characters from parents to the next generation.
- DNA molecules are composed of DNA and protein, and functional segments of DNA are called genes.
- The nucleus plays a central role in cellular reproduction, determining the way the cell will develop and what form it will exhibit at maturity.
Cell Organelles
- Eukaryotic cells have membrane-bound cell organelles, including the endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and plastids, each performing specific functions for the cell.
- Prokaryotic cells lack most of these organelles and have a poorly defined nuclear region called a nucleoid.
- The endoplasmic reticulum (ER) is a network of membrane-bound tubes and sheets involved in protein synthesis, transport, and lipid synthesis.
- The Golgi apparatus consists of a system of membrane-bound vesicles (flattened sacs) arranged approximately parallel to each other in stacks called cisterns, involved in packaging and dispatching of products.
- Lysosomes are membrane-bound sacs filled with digestive enzymes, acting as a waste disposal system for the cell, digesting foreign materials and worn-out organelles.
- Mitochondria are known as the powerhouses of the cell, generating energy for the cell through ATP production, and having their own DNA and ribosomes.
- Plastids are present only in plant cells, involved in photosynthesis, and can be classified as chromoplasts (colored plastids) or leucoplasts (white or colorless plastids).
- Vacuoles are membrane-bound sacs containing cell sap, providing turgidity and rigidity to the cell, and storing substances of importance in plant cells.
Cell Division
- Cell division is the process by which new cells are formed in organisms to grow, replace old cells, and form gametes required for reproduction.
- The cell is the fundamental structural and functional unit of living organisms.### Cell Structure and Function
- The fundamental organisational unit of life is the cell.
- Cells are enclosed by a plasma membrane composed of lipids and proteins.
- The cell membrane is an active part of the cell, regulating the movement of materials between the cell and its environment.
- Plant cells have a cell wall composed mainly of cellulose, located outside the cell membrane, which enables them to exist in hypotonic media without bursting.
Nucleus and ER
- The nucleus in eukaryotes is separated from the cytoplasm by a double-layered membrane and directs the life processes of the cell.
- The ER functions both as a passageway for intracellular transport and as a manufacturing surface.
Golgi Apparatus and Plastids
- The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification, and packaging of substances manufactured in the cell.
- Most plant cells have large membranous organelles called plastids, which are of two types: chromoplasts and leucoplasts.
- Chromoplasts, which contain chlorophyll, perform photosynthesis, while leucoplasts function in storage.
Vacuoles
- Vacuoles are storage sacs for solid or liquid contents.
- Plant cells have very large vacuoles, with the central vacuole occupying 50-90% of the cell volume.
- Vacuoles help maintain the turgidity of the cell and store important substances, including wastes.
Cell Division
- Cells divide for growth of the body, replacement of dead cells, and formation of gametes for reproduction.
- 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 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 of the mother cell.
Prokaryotic and Eukaryotic Cells
- Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles.
- Eukaryotic cells have membrane-bound organelles and a true nucleus.
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Description
Explore the fundamental unit of life, cellular structure, and learn about Robert Hooke's discovery of cell structure while examining cork.
