Title 2.1N Cells.pdf ✅

SACE Stage 2 Biology 1 2.1 CELLS LEARNING OBJECTIVES Cells The cell theory unifies all living things. Cell membrane The cell membrane separates the cell cytoplasm from its surroundings and controls the exchange of materials, including nutrients and wastes, between the cell and its environment. • Describe and represent the fluid mosaic model of the cell membrane. Prokaryotic cells The major types of cell are prokaryotic and eukaryotic Prokaryotic and eukaryotic cells have many features in common, which is a reflection of their common evolutionary past. • Compare prokaryotic and eukaryotic cells with respect to their size, internal organisation, and shape/location of chromosomes Prokaryotes only exist as single cells. Eukaryotic cells Eukaryotic cells have specialised organelles which facilitate biochemical processes. • Represent the structure and describe the function of: – Nucleus, nucleolus, mitochondrion, chloroplast, vacuole/vesicle, Golgi body, endoplasmic reticulum (rough and smooth), ribosome, lysosome, cytoskeleton. • Compare the structures of plant and animal cells. CELLS AND LIVING THINGS The characteristics of living things can be remembered with “MRS GREN” Component Example Movement Cells can move around in their environment Respiration / metabolism Chemical reactions occur within cells. Cells use proteins to carry out almost all of their metabolic functions. Cellular respiration – cells use glucose to produce energy for themselves. Sensitivity / homeostasis Cells can detect and adapt to changes in their environment. Growth Increase in cell size (unicellular) Increase in cell number (multicellular) Reproduction Asexual reproduction Sexual reproduction Excretion Cells can get rid of their wastes, which are unwanted products from metabolism Nutrition Intake / production of organic molecules, which can be broken down for energy
SACE Stage 2 Biology 2 All living things are made up of one or more cells. These are microscopic units of life which, when put together, can make up larger organisms. The cell is the smallest unit of life – this means that anything smaller than a cell cannot be living. The cell theory is a theory which unifies all living things, and is made up of 3 components: Cell theory 1. All living things are comprised of one or more cells 2. The cell is the basic unit of life 3. All cells come from pre-existing cells CELL MEMBRANE All cells are bounded by a thin cell membrane, which holds the contents of the cell in place. Fungi, bacteria and plants also have an additional cell wall layer, which gives the cell structure. STRUCTURE OF THE CELL MEMBRANE The cell membrane is made up of a phospholipid bilayer with embedded proteins arranged in a fluid mosaic structure. A phospholipid is a structure which is made up of a phosphate ‘head’ and two lipid ‘tails’ • Phosphate head: hydrophilic, which means that it readily associates with water molecules. • Lipid tails: hydrophobic, which means that they do not readily mix with water. Component Definition Phospholipid bilayer The cell membrane is made up of two layers of phospholipids, with the hydrophilic phosphate ‘heads’ facing outwards and the hydrophobic lipid ‘tails’ facing inwards. Phospholipids arrange themselves into a bilayer so the lipid tails avoid interacting with water on either side of the membrane. Embedded proteins The phospholipid bilayer also has embedded proteins, which are organic molecules which carry out cellular functions. There are two classes of proteins: • Integral membrane proteins – go all the way through the phospholipid bilayer, function as transport proteins • Peripheral membrane – do not go all the way through the phospholipid bilayer, function as receptors Cholesterol Increases rigidity at membrane face, and decreases rigidity in membrane core. Generally, cholesterol helps to regulate membrane fluidity in fluctuating temperatures.
SACE Stage 2 Biology 3 The cell membrane is said to have a fluid-mosaic structure: The Fluid-mosaic model of cell membranes Fluid refers to the phospholipids which make up the cell membrane not being fixed in place, which means they can move around freely. Mosaic refers to proteins embedded in the phospholipids, which can also move around The cell membrane has three primary functions: • Boundary: defines the boundary of the cell and holds cellular contents inside the cytoplasm. • Barrier: controls entry and exit of substances into the cell, which allows the cell to facilitate the exchange of nutrients and wastes with the environment. • Semipermeable: some substances can enter/exit more easily than others. TYPES OF CELLS Organelles are components inside cells which perform specialised functions, like human organs inside a human. • Membrane-bound organelles: surrounded by an additional cell membrane • Non-membrane bound organelles: not surrounded by an additional cell membrane Cells which have membrane bound organelles are more complex because these membrane partitions allow them to maintain different environment in each compartment, and hence optimise a specialised metabolic process in each compartment. We can classify cells as prokaryotic and eukaryotic based on the presence of membrane-bound organelles. Prokaryotic Eukaryotic What are they? Simple cells which are older in evolutionary terms. Can only exist as unicellular organisms. Bacteria More complex cells which evolved from prokaryotic cells. Can exist as unicellular or multicellular organisms. Animals, plants, fungi Size Small cells (1 – 10 μm) Larger (10 – 200 μm) Nucleus and DNA No nucleus. DNA (a type of nucleic acid) is located in the nucleoid region of the cytoplasm. DNA is a single circular chromosome not complexed with histones. DNA can exist in circular loop known as a plasmid Nucleus present. DNA is located in the nucleus. DNA is many linear chromosomes, complexed with histone proteins. Organelles No membrane-bound organelles. Membrane bound organelles. Cell division Divides via binary fission. Divides via mitosis or meiosis.
SACE Stage 2 Biology 4 PROKARYOTIC CELLS Prokaryotic cells are smaller, simple cells which have no membrane-bound organelles or nucleus. Component Structure Function Cell membrane Phospholipid bilayer with embedded proteins and cholesterol. Regulates transport of materials into/out of cell. Embedded proteins function as receptors, cell adhesion, etc. Cytoplasm Fluid component composed of water with suspended/dissolved proteins, lipids, carbohydrates, nucleic acids, ions. Holds organelles in place. Site of metabolic activity – contains compounds required for reactions. Cell Wall Rigid structure which forms a layer outside the plasma membrane. Gives cell shape and protects the cell from the environment. Mesosome Infolding of the cell membrane Site of cellular respiration. Ribosomes Very small complexes of RNA and proteins. Synthesis of proteins. Plasmid Circular DNA, not involved with reproduction; only the chromosome has the information for cell division or binary fission. DNA contains information for protein synthesis. Nucleoid Region in the cytoplasm where the DNA is found. Flagella ‘Tail’ like structures outside the cell. Allows cell to move around. Pili ‘Hair’ like structures attached to cell wall Cell attachment