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BIOLOGY CHAPTER 2

QuestionAnswer
Cells the basic functional units of living organisms
Eukaryote cell or organism with a membrane bound nucleus and organelles. Examples are plants and animals. Linear DNA chromosomes. Usually multicellular
Prokaryote cell or organism without a membrane bound nucleus and organelles. Examples are bacteria and cyanobacteria. Lack membrane organelles and has single cellular DNA. Usually unicellular, plasma membrane surrounded by outer cell wall. Smaller, may have flagella
Organelles membrane bound structures that carry out specific functions in the cell. Ribosomes are an exception as they are not membrane bound but still an organelle. Cytoplasm = cytosol + organelles. Cytosol = fluid component
Nucleus Spherical with double membrane. Nuclear membrane has many holes called nuclear pores which allows selective passage of substances. Contains genetic information used for the synthesis of proteins and control cellular processes
Mitochondia located in cytoplasm. Has an outer and highly folded inner membrane (cristae) with matrix being the space inside the folds. Contains mDNA. Site of ATP synthesis by releasing energy in aerobic respiration
Ribosomes Site of protein synthesis. Proteins produced on rough ER are transported away from cell, ones made on free ribosomes are used within cell. Located in cytoplasm or bound to ER. Not enclosed by membrane but made of rRNA and proteins
Rough ER Synthesis, modification and packaging of proteins, and transports them within the cell. Continuous with nuclear membrane into the cytoplasm. Complex structure of flattened membranous sacs with ribosomes
Smooth ER Synthesis of lipids including oils, phospholipids and steroids. Metabolises carbohydrates and transports these material through the cell. Same structure as rough except no ribosomes and in cytoplasm
Golgi apparatus Further processes and packages proteins into vesicles for export from the cell. Located in cytoplasm and is a stack of flattened membraneous sacs (cisternae)
Lysosomes Lysosomes use their enzymes to destroy unwanted cells parts or damaged molecules from within or outside the cell by engulfing it. Located free in the cytoplasm and are single membrane bound sac of digestive enzymes and bud off golgi apparatus
Vacuoles membrane bound fluid filled spaces in most cells but larger in plants. In plants they are structural support for cell and storage and in animals are storage of enzymes for intracellular digestion
Chloroplasts (Plants) Site of photosynthesis. Located within the cytoplasm of plant leaf and sometimes stem. Outer and inner membrane
Cell wall (Plants) Protects the cell, maintains cell shape and prevents excessive water uptake. Lies outside the cell membrane and is made up of cellulose
Atom building block of matter
Molecule Two or more atoms
Element Molecules that consist of the same type of atom
Compound molecule consisting more than one type of atom
Polar have positive and negative regions. They have an unequal distribution of electrons with one side is more negative than the other side. Polar molecules readily dissolve in water- water soluble/hydrophilic
Non-polar non-polar molecules have an even distributed of charge and are neutrally charged- they are symmetric. Non-polar molecules are lipid-soluble/hydrophobic
Ions atom that has lost or gained an electron and so has a net electric charge
Organic compounds Organisms produce compounds that contain carbon and hydrogen known as organic compounds. The four main groups of organic compounds are- • carbohydrates, • proteins • nucleic acids and • lipids
Biomacromolecules Carbohydrates, proteins and nucleic acids are huge and are also known as biomacromolecules They are chain- like molecules called polymers, formed by joining together many smaller units (monomers) to form a chain.
Inorganic compounds All other compounds, whether in living or non-living things. Inorganic substances that are important for living organisms include water, oxygen, carbon dioxide, nitrogen and minerals
Carbohydrates •Source of chemical energy. • Used as energy reserves • Form structural components such as cell walls • Form part of both DNA and RNA • Combine with proteins & lipids to form glycoproteins and glycolipids that are found in cell membranes.
Monosaccaride Molecule that comprises a single sugar, usually has the formula C6H12O6. There are many monosaccharides like glucose, galactose and fructose. They have the same molecular formula, different structural formula (how the atoms are arranged).
Dissaccaride A disaccharide is formed when two monosaccharides combine. Examples include- • Sucrose (cane sugar) = glucose + fructose • Lactose (milk sugar) = galactose + glucose • Maltose= glucose + glucose
Polysaccharides Polysaccharides are polymers of sugar molecules. Examples of polysaccharides include- • Glycogen • Starch- Form of energy storage in plants • Cellulose
Lipids • as the main component of plasma membranes and organelle membranes (as phospholipids) • storing energy (fats and oils) • role as hormones A fat molecule is made of two kinds of molecules- fatty acids and glycerol. (non-polar and hydrophobic).
Phospholipids two fatty acids and a phosphate group attached to a glycerol molecule. Phospholipids make up the cellular membrane. They are major component of cell membranes.
Triglycerides composed of a 3 fatty acid molecules and a glycerol molecule
Steroids e.g. hormones and vitamins
Nucleic acids genetic material of all organisms, determines many of the features of an organism. Monomer: nucleotides - nucleotide consists of a phosphate, a sugar and a nitrogen base. Polymer: Nucleic acid
Deoxyribonucleic acid (DNA) DNA carries the ‘instructions’ required to assemble proteins from amino acid subunits using a genetic code. It is passed accurately from cell to cell during cell division. The four bases in DNA are adenine (A), thymine (T), guanine (G) and cytosine (C).
Ribonucleic acid (RNA) RNA plays a major role in the manufacture of proteins within cells. The four bases in RNA are adenine (A), uracil (U), guanine (G) and cytosine (C).
Proteins Functions: • Catalyse cellular reactions (enzymes) • Communicate information (hormones) • Carrier molecules (e.g. haemoglobin with oxygen) • Structural components of cells (e.g. collagen) • Defence against disease • Contractile (muscle movement)
Proteins monomers and polymers Monomer: amino acid The general formula of an amino acid is • An amino group • Variable R group and • Carboxyl group. Polymer: polypeptide (protein)
Plasma membrane *encloses the contents *controls the movement of substances between the exterior (the extracellular fluid) and the interior of the cell (the cytoplasm). *Semi–permeable *cell recognition and communication
Fluid mosaic model According to this model, plasma membranes consist of two layers of phospholipid molecules, with other molecules including proteins, carbohydrates and cholesterol scattered throughout the membrane
Structure of plasma membrane comprises of a phospholipid bilayer into which proteins and glycoproteins protrude – these allow certain substances to pass across the membrane in either direction.
Phospholipids composed of a hydrophilic head containing a phosphate group and glycerol, and two hydrophobic fatty acid tails. The impermeability of membranes to water-soluble (hydrophilic) molecules is due to the phospholipid bilayer.
integral proteins embedded in the phospholipid bilayer. Typically, they span the width of the plasma membrane with part of the protein being exposed on both sides of the membrane. Proteins like this are described as being transmembrane proteins.
peripheral proteins not embedded in the phospholipid bilayer. Bind to integral proteins or penetrate into one surface of PM. Attached either to phospholipid molecules or integral proteins. Function as enzymes, receptors, structural attachment points & recognition sites.
Carbohydrates associated with plasma membranes linked to protruding integral proteins (forming glycoproteins) or to lipids (forming glycolipids) on the outer surface of the membrane. Play a role in recognition and adhesion between cells, and recognition of antibodies, hormones and viruses by cells
Fluid nature of the plasma membrane Lipid molecules are free to move about within the layers. Molecules are not fixed in place. Most of the phospholipids and some of the proteins can move about laterally, and molecules are able to flip- flop transversely across the membrane
Factors that alter the fluidity of the plasma membrane - the presence of cholesterol makes the bilayer more stable, without it the membrane breaks down. Also decreases the permeability of the membrane. The cholesterol molecules restrict the movement of the phospholipid molecules, prevent them from packing together as closely
Factors that alter the fluidity of the plasma membrane - temperature As temperature increases, the fluidity of plasma membranes increases. This is because the phospholipids become less closely packed together and are able to move more freely
Membranes in organelles membrane surrounding the organelle is to control the movement of substances between the organelle and the cytosol, ensuring the organelle contains the substances it requires for its function. This is known as compartmentalisation in eukaryotic cells
Benefits of membranes in organelles optimises efficiency of processes by grouping enzymes & reactants for a particular function together in high concentrations & at the right conditions, Enables incompatible reactions to be performed within a cell by separating the processes, or reactions
Movement of material across membranes - oxygen, carbon dioxide small uncharged molecule permeable
Movement of material across membranes - steroids, alcohol, chloroform lipid-soluble, non-polar molecule permeable
Movement of material across membranes - water, urea small polar molecule permeable or selectively permeable
Movement of material across membranes - potassium ion (K+) sodium ion (Na+), chloride ion (Cl–) small ion non-permeable (ions pass through protein channels)
Movement of material across membranes - amino acid, glucose large, polar, water-soluble molecule non-permeable (molecule passes through protein channels)
Hydrophilic molecules impermeable to plasma membrane • most water-soluble molecules • ions • Large polar molecules • Extremely small polar molecules, such as urea, are able to pass between the phospholipid molecules however it occurs slowly.
Passive Transport The movement of molecules across the plasma membrane without the expenditure of energy is known as passive transport.
Diffusion Diffusion is the net movement of a substance from an area of high concentration to an area of low concentration. This process does not require energy (passive).
Osmosis Definition: Net movement of water from an area of high concentration of water, to an area of low concentration of water. This process also does not require energy.
Isotonic solutions The solutions being compared have equal concentrations of solute
Hypertonic solution The solution with the higher concentration of solute (hence lower concentration of free water molecules)
Hypotonic solution The solution with the lower concentration of solute (hence higher concentration of free water molecules)
Facilitated Diffusion Net movement of a substance from an area of high concentration to an area of low concentration through selective protein channels.
Channel proteins Each channel protein consists of a narrow water- filled pore in the plasma membrane. This creates a hydrophilic passage across the plasma membrane that bypasses the phospholipid bilayer and facilitates the diffusion of charged particles
Carrier proteins bind the molecules being transported causing the protein to undergo changes in shape that allow specific molecules to be transported across the membrane. After the molecule has crossed the membrane, the protein is restored to its original shape
Factors that affect passive transport - concentration the greater the difference in concentration gradient, the faster the rate of diffusion. When the concentration is equal on both sides of the membrane the net diffusion is zero, even at high temperatures
Factors that affect passive transport - temperature the higher the temperature, the higher the rate of diffusion. Increasing the temperature increases the speed at which molecules move
Factors that affect passive transport - particle size the smaller the particles, the faster the rate of diffusion through a membrane
Active transport Net movement of dissolved substances through a membrane from a region of low concentration to region of high concentration with the assistance of energy input and specific transport proteins
Bulk transport Large molecules, such as proteins and polysaccharides, as well as cellular waste products, nutrients and water, can be transported in bulk across the membrane by exocytosis and endocytosis. Like active transport, bulk transport requires energy
Endocytosis The bulk uptake of substances by regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle
phagocytosis cell engulfs a solid material
pinocytosis the plasma membrane engulfs liquid that contains dissolved molecules
Receptor-mediated endocytosis type of pinocytosis that engulfs specific substances. Protein receptors located on the surface of the plasma membrane respond to particular molecules, binding to the molecule and then triggering the engulfment of the substance into the cell
Exocytosis The bulk secretion of substances by the fusion of intracellular vesicles with the plasma membrane
Created by: emmawalton05