unit 2 bio (cells) Flashcards
characteristics of eukaryotic cells
- have a nucleus
- contain membrane bound organelles
- larger cell size
function of the nucleus
controls cell activities such as growth and the repair of worn out parts
contains chromosomes: long, thread-like structures made up of DNA which stores hereditary information
contains nuclear membrane: separates contents of nucleus from the rest of the cytoplasm; contains nuclear pores and has 2 layers of membranes
function of cell surface membrane
partially permeable membrane made up of lipids and proteins
controls the movement of substances in and out of the cell
function of cytoplasm
jelly like substance that fills up the cell; site of cell activities and contains organelles that perform a specific job within the cell
function of cellulose cell wall
protects cell from injury and gives the cell a fixed shape
function of rough endoplasmic reticulum
surface is studded with ribosomes which give it a rough appearance
modifies proteins made by ribosomes
function of smooth endoplasmic reticulum
tubular, smooth, appearance due to absence of ribosomes attached to its surface
synthesises substances like fats and steroids and converts harmful substances into harmless substances through detoxification
function of ribosomes
synthesise proteins in the cell
ribosomes attached to RER make proteins that are usually transported out of the cell
ribosomes lying freely in cytoplasm make proteins that are used within the cytoplasm of the cell
function of golgi body
cup shaped compartments known as cisternae
chemically modifies substances made by endoplasmic reticulum
stores and packages vesicles for secretion out of the cell or to other organelles in the cell
process of secretion of substances in golgi body
- vesicles containing polypeptide made by RER pinch off from the RER
- vesicles fuse with golgi body and release the molecules made by the ER into it. the substances may be modified by the golgi body
- secretory vesicles containing modified substances pinch off from the golgi body and move towards the cell surface membrane
- secretory vesicles fuse with the cell surface membrane and their contents exit the cell
function of mitochondria
contains a double membrane that surrounds a matrix, inner membranes fold inwards to form cristae
site of aerobic respiration where food substances are broken down to release energy in the form of ATP, which may be used to perform activities such as cell growth and reproduction
function of chloroplasts
double membranes enclose a fluid filled space called the stroma, and the 3rd inner membrane (thylakoid membrane) forms the thylakoid. stacked thylakoid is known as granum
contains chlorophyll necessary for photosynthesis to occur
function of vacuoles
fluid filled space enclosed by a partially permeable membrane
stores substances within a cell
plant cell vacuoles vs animal cell vacuoles
plant: large, central vacuole that contains cell sap consisting of sugars, mineral salts, and amino acids + serves as disposal of waste materials
animal: numerous small vacuoles that store water and food substances
adaptations of muscle cells
- contain many mitochondria: provide energy for contraction of muscle cells
- contain contractile protein fibres: fibres contract and relax to bring about movement
- contain many nuclei: allow for cell division
adaptations of root hair cells
long and narrow extension: increases surface area to volume ratio of cell for increased rate of absorption of water and mineral salts via osmosis and diffusion
low water potential in vacuole: allow for osmosis of water into cell
adaptations of red blood cells
biconcave shape: increase surface area to volume ratio of the cell for increased rate of oxygen uptake
flexible: allows cells to squeeze through narrow blood capillaries easily
contains haemoglobin: binds to oxygen easily to transport it around the body
no nucleus: to contain more haemoglobin to transport more oxygen
definition of diffusion
net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient
what is facilitated diffusion
diffusion of substances through cell membranes using specific protein channels or carriers from regions of higher concentration to regions of lower concentration
- carrier mediated: via protein carrier
- channel mediated: through a protein channel, mostly ions
factors affecting rate of diffusion
concentration gradient
diffusion distance
surface area to volume ratio
definition of osmosis
net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially/selectively permeable membrane down a water potential gradient
effects of high water potential on plant cells
- cell sap in vacuole has lower water potential than surrounding solution
- net movement of water molecules into the cell via osmosis
- cell expands and becomes turgid
- cell wall prevents cell from bursting as cytoplasm volume increases
effect of low water potential on plant cells
- cell sap in vacuole has higher water potential than surrounding solution
- net movement of water molecules out the cell via osmosis
- cell becomes flaccid and limp
- vacuole decreases in size, cytoplasm shrinks away from cellulose cell wall, cell surface membrane pulls away from cell wall and becomes plasmolysed
effect of high water potential on animal cells
- cytoplasm has lower water potential than surrounding solution
- net movement of water molecules into the cell via osmosis
- cell expands and bursts
effect of low water potential on animal cells
- cytoplasm has higher water potential than surrounding solution
- net movement of water molecules out of the cell via osmosis
- cell shrinks in size and becomes crenated
definition of active transport
the process in which cellular energy in the form of ATP is used to move the particles of a substance from a region of lower concentration to a region of higher concentration across a membrane against a concentration gradient
chemical composition of proteins
- made up of carbon, hydrogen, oxygen, nitrogen, and sulfur
- contain a basic amino group (NH2), an acidic carboxyl group (-COOH), and a variable R-group
- general formula: R-CH-NH2-COOH
function of proteins
- growth and repair of worn out body cells
- synthesis of new cytoplasm
- synthesis of enzymes, hormones, and antibodies to combat diseases
levels of organisation of proteins
primary structure: unique number and sequence of amino acids held together by peptide bonds that make up a polypeptide chain
secondary structure: folding and coiling of parts of the polypeptide to form alpha helices or beta-pleated sheets
tertiary structure: overall unique 3d structure of the polypeptide held together by hydrogen, ionic, disulfide bonds and hydrophobic interactions
quarternary structure: when two or more polypeptide chains join together to form a biologically functional protein
chemical composition of carbohydrates
contain carbon, hydrogen, and oxygen atoms (h and o atoms present in 2:1 ratio)
general formula: Cx(H2O)y
functions of carbohydrates
- used as substrate for respiration to provide energy for cell activities
- to form supporting structures
- for formation of nucleic acids
name monosaccharides
glucose, galactose, fructose
name disaccharides
maltose, lactose, sucrose
name polysaccharides
glycogen, starch, cellulose
chemical composition of fats
made up of carbon, hydrogen, and oxygen
no general formula
functions of fats
- long-term storage of energy
- insulating and prevents excessive heat loss
- solvent for fat soluble vitamins and other vital substances
- reduces water loss from skin surface when oils form a layer over it
what are enzymes
biological catalysts that speed up the rate of a chemical reaction and remain chemically unchanged at the end of the reaction
characteristics of enzymes
- speed up the rate of chemical reactions by lowering the activation energy needed to start the reaction
- specific in action
factors affecting efficiency of enzymes
temperature
pH
how does low temperature affect enzymes
kinetic energy of molecules is low, hence enzyme and substrate molecules move slowly. there is a decrease in the rate of collisions between enzyme and substrate molecules, less enzyme substrate complexes are formed
how does high temperature affect enzymes
high temperatures break the bonds that keep enzymes in their specific shape. their active sites lose their original shape and are no longer complementary to the substrate. enzymes become denatured and lose their catalytic function
how does change in pH affect enzymes
changes in pH alter the shape of the active sites of the enzyme, causing active sites to lose their original shape. active sites are no longer complementary to the substrate, and enzyme-substrate complexes cannot be formed. the enzyme is denatured and lose their catalytic function
process of enzyme breaking down substrate
- upon effective collisions between the substrate and the active site of the enzyme, an enzyme-substrate complex is formed
- reactions take place at the active site to convert substrate molecules into product molecules
- products separate from the enzyme which remains unchanged and is free to bind with more substrate molecules
- when reaction is completed, products no longer fit into the active site of the enzyme
