Class notes
cell ultrastructure notes
- Course
- Life Sciences
- Institution
- 10th Grade
Grade 10 IEB cell ultrastructure notes
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Cell Ultrastructure 1What are cells?
Cells are the basic units of life. All living things are made up of individual cells that
are each alive. This means that the cell is the smallest living thing. Some living
things are made up of only one cells and they are unicellular. Unicellular organisms
are too small to be seen without the use of a microscope. Cells are the building
blocks of living organisms. Our bodies are made up on 200 different types of cells
Animal cells are usually surrounded by a fluid medium. This environment is called
tissue fluid. A process called homeostasis helps maintain the constant internal
environment of most animals.
Flow diagram showing breakdown of a cell
The cytoplasm
• Background substance of the cell.
• Composed of mainly water and proteins but also has many dissolved substances in
• Has minerals, organic substances (e.g. sugars and amino acids) and gases
• Mixture forms the type of suspension called a colloid
• Some colloids (like the cytoplasm) have particular properties. They can: change from a gel
(jelly state) to a sol ( liquid state) and vice versa; Imbibe (take up) water; remain fairly stable
(i.e. do not separate)
• As cytoplasm is a colloid, it too has these properties.
• Sol-gel changes occur continually. Outer layer of cytoplasm tends to be gel (semi-solid) and
often referred to as cytogel
• Inner part tends to be sol (liquid) and often referred to as cytosol
• the cytoplasm moves constantly around the cell – this is called cyclosis
• the process of imbibition helps the cell to absorb water, water is a critical constituent of
cytoplasm
• cytoplasm is stable and does not separate into its component parts. Particles remain
suspended ( distributed) in cytoplasm
Animal cells
• Sedentary – don’t move around
• Do not have cells walls or chloroplasts
• Do not have fixed shaped bc they don’t have a large vacuole
• Usually has more smaller vacuoles
Plant cells
• Sedentary – don’t move around
• Has a cell wall and chloroplasts
, Cell Ultrastructure 2
• Rigid shape because of large vacuole and cell wall
• Xylem (carries tissue around) in the cell wall
Organelles
Plasma membrane/ cell membrane
• Acts as “security fence” around the cell and surround
the entire cell
• Selectively permeable – controls what goes into and out
of cell.
• Three very thin layers (dark-light-dark) – made up of
protein and lipids (fats)
• Lipids are called phospholipids and each have a
water attracting (hydrophilic) and two water
repelling (hydrophobic) tails
• Proteins embedded in lipid bilayer
• Double layer – phospholipid bilayer
• Described at a fluid mosaic – explains the dynamic (constantly moving) properties of the
membrane
• Proteins are “transporters” transporting other molecules across the membrane, this is called
active transport and needs energy.
• Water moves through the membrane without the help of the proteins, this is passive
movement and needs no energy.
• Water only moves by diffusion, from high to low concentration.
The Nucleus
• Every true eukaryotic cell has a nucleus, the nucleus is the
largest organelle and a cell without a nucleus, can only life for a
very short time.
• Spherical shape and is between 10 and 20 micrometers in length
• The nucleus is surrounded by a double nuclear membrane
called the nuclear envelope that has small nuclear pores.
• Contains a substance called nucleoplasm (very similar structure
to cytoplasm)
• Nucleoplasm is continuous with cytoplasm through the nuclear pores
• Nucleolus makes ribosomes for protein synthesis, nuclear pores are the opening
• The nucleus contains chromatin material (DNA threads) and nucleolus
• The DNA only becomes visible with a light microscope during cell division, when it condenses
to form chromosomes.
• Outer membrane is continuous with another cell structure called the endoplasmic reticulum
• Nucleus controls cells activities. Genetic material of the nucleus is called DNA and holds
instructions for all cell activity.
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