biology paper 1

• osmosis is the movement of water molecules through a partially permeable membrane from a region of high water concentration to lower water concentration
• the process of osmosis can be reversed by applying pressure, this is called reverse osmosis
• water molecules can pass both ways through the membrane because water molecules move about randomly
• since there are more molecules are on one side of the membrane than the other, that means theres a steady net flow of water into the region of fewer water molecules
• stronger solution = more dilute. water acts like its trying to "even up" the concentration on either side of the membrane
• first 3 steps of osmosis practical

  1. cut potato(anything) into identical cylinders, get beakers with different sugar solutions; one pure water, another very concentrated sugar solution. 2. measure mass of cylinders then leave one cylinder in each beaker for certain amount of time 3. take cylinders out, dry them with paper towel and measure mass again.
• results of osmosis practical

  4. if cylinders draw in water by osmosis, they'll increase in mass. If water drawn out, they'll decrease in mass. 5. dependent variable is chip mass, independent is concentration, control is temp, vol of solution.
• active transport - movement of substances against their concentration gradients using energy stored in ATP
• concentration gradient - difference between concentrations of solute particles across a semi-permeable membrane
• errors possible in osmosis practical


  if cylinders not fully dried = excess water would give a higher mass. If water evaporated in beakers, concentrations of sugar solutions would change.
• describe the first 3 stages of the cell cycle- growth + DNA replication

  1. in cells that arent dividing, dna is spread out in long strings. 2. before division, cell has to grow and increase amount of subcellular structures such as mitochondria and ribosomes. 3. then dna is duplicated- theres one copy for each new cell. dna is copied and forms x-shaped chromosomes. Each arm of the chromosome is an exact duplicate of each other
• describe the last 3 stages of cell cycle- mitosis


  4. Chromosomes line up at centre of cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell. 5. Membranes form around each set of chromosomes- becoming the nuclei of each the two new cells- nucleus has divided. 6. cell has now produced 2 new daughter cells. daughter cells contain exactly the same DNA ( identical ). Their DNA is also identical to the parent cell.
• nucleus contains genetic material in the form of chromosomes
• chromosomes are coiled up lengths of DNA molecules
• each chromosome carries a large number of genes. different genes control development of different characteristics
• the stage of the cell cycle where the cell divides is called mitosis
• differentiation is the process where a cell changes to become specialised for its job
• as cells change they develop different subcellular structures and turn into different types of cells. this allows them to carry out different specific functions
• stem cells can divide many times without changing, so they can be used to replace damaged or diseased tissue
• embryonic stem cells have the potential to develop into any type of body cell
• a stem cell has the potential to develop into any type of body cell
• most differentiation occurs as an organism develops
• in most animal cells, the ability to differentiate is lost at an early stage after they become specialised
• plants never lose the ability to differentiate
• undifferentiated cells are known as stem cells
• sperm cells are specialised for reproduction
• the function of sperm is to get the male DNA to the female DNA
• sperm cells have long tails and stream lined head to help it swim to the egg. there are also lots of mitochondria in the cell to provide the enrgy needed. also carries enzymes in its head to digest through the egg cell membrane
• nerve cells are specialised for rapid signalling
• function of nerve cells is to carry electrical signals from one part of the body to another
• nerve cells are long to cover more distance and have branched connections at their ends to connect other nerve cells and form a network throughout the body
• muscle cells are specialised for contraction
• function of a muscle cell is to contract quickly
• muscle cells are long so that they have more space to contract and contain lots of mitochondria to generate energy needed for contraction
• root hair cells are specialised for absorbing water and minerals
• root hair cells are on the surface of plant roots which grow into long hairs that stick out into the soil, this gives the plant a big surface area for absorbing water and mineral ions from the soil
• phloem and xylem cells are specialised for transporting substances
• phloem and xylem cells form phloem and xylem tubes which transport substances like food and water around the plants. to form the tubes the cells are long and and joined end to end
• xylem cells are hollow in the centre and phloem cells have very few subcellular structures so that stuff can flow through them
• eukaryotic cells are complex and include all animal and plant cells