Cells and Cell Processes
Characteristics of Living Organisms
Movement – Action by organism causing change in position/place
Respiration – Chemical reactions in cells which break down nutrient molecules and release energy for
metabolism (life sustaining chemical reactions in organism)
Sensitivity – Ability to sense and react to stimuli in internal/external environment
Growth – Permanent increase in size by increase in number of cells, cell size or both
Reproduction – Able to perform processes that make more of the same type of organism
Excretion – Removal of waste products of metabolism, toxic materials, and substances in more amount
than required
Nutrition – Taking in materials for energy, growth, development. Plants need light, CO2, water and ions.
Humans need organic compounds, ions and usually water
Parts of the Cell
1. Cell Membrane (Both) – Partially permeable membrane around cell, controls substances entering
in and out of cell; one of the most important is water. All other substances pass through in solution
2. Cytoplasm (Both) – Jelly-like substance in which chemical reactions of cell take place. Contains nucleus
3. Mitochondria (Both) – Site of aerobic respiration (job is to convert energy). Where cell turns
glucose and oxygen into energy. Cells with high rates of metabolism require more mitochondria to
provide enough energy.
4. Nucleus (Both) – Contains DNA of the cell. Determines what the cell will be. Controls cell activities
5. Vacuole (Plant only) – Is a space full of cell sap, a solution made of mainly sugars. Vacuole helps
maintain turgor pressure of cell
6. Cell Wall – Cellulose ‘box’ which contains cell. Helps maintain cell shape, prevent cell from bursting
as it absorbs water.
7. Chloroplasts (Plant only) – Contain pigment chlorophyll (absorbs light). Are site of photosynthesis
8. Ribosomes (Both) – Assemble amino acids to form specific proteins (Protein Synthesis). Can be
found in cytoplasm, or attached to Rough Endoplasmic Reticulum (ER).
9. Vesicles (Both) – Break away from Endoplasmic Reticulum, used to transport proteins from ER to
other places.
Levels of Organisation (Ascending)
1. Tissue – Group of cells with similar structure working together to perform same function
2. Organ – Structure made of group of tissues, working together to perform specific functions
Cells and Cell Processes
3. Organ System – A group of organs with relating functions, working together to perform body
functions
a. Digestive system, Urinary system
Specialised Cells
1. Ciliated Cells – Movement of mucus in trachea and bronchi. Have cilia which are constantly in a
flicking motion which creates stream of mucus to carry dust and bacteria away from lungs
2. Goblet Cells – Found in trachea and bronchi, form and secrete mucus
3. Root Hair Cells (Plants only) – Absorption of water and nutrients from soil. Have large surface area
for more absorption. Thin cell membrane for quick intake
4. Xylem Vessels (Plants only) – Carry water and minerals from roots to leaves via the stem. Long,
hollow to carry water. Rings of lignin in walls strengthen to withstand pressure of water
5. Palisade Mesophyll Cells (Plants only) – Perform photosynthesis. Packed with chloroplasts for
maximum photosynthesis. Cells tall, closely packed for more light absorption
6. Nerve Cells – Carry and deliver impulses. Long and thin for quick transport
7. Red Blood Cells – Carry maximum oxygen for respiration. No nucleus gives more space for more
haemoglobin to carry oxygen. Biconcave shape for more surface area = more oxygen absorbed.
8. Sperm – Reproduction – Tail of sperm allows it to swim in ovum. Section behind has mitochondria
to give sperm energy to swim
Diffusion – Net movement of particles from an area of high concentration to low concentration, due to
their random movement. (Down a concentration gradient)
Factors affecting Diffusion
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Surface Area to Volume ratio – Large surface area = faster diffusion. Larger volume = slower diffusion
Temperature – Higher temperature means molecules have more Ek to diffuse
Diffusion Distance – Small distance for molecules to diffuse = fast diffusion
Osmosis – Diffusion of water from a region of higher water potential (dilute solution) to lower water potential
(concentrated solution) through a semi-permeable membrane.
Active Transport – Movement of particles from a region of lower concentration to higher concentration
through a semi-permeable membrane using energy from respiration. Example is when plant absorbs ions (like
nitrate ions) from soil using active transport, since there’s a higher concentration of the ions in the plant than
soil.
Catalyst – Substance which increases the rate of chemical reactions and is not changed by the reaction
Enzymes – Proteins which act as biological catalysts
Factors affecting Rate of Enzyme Activity
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pH – Changes in pH can alter shape of the enzyme. When enzyme exposed to extreme pH it is
denatured and shape of active site is changed, so it cannot function anymore
Temperature – Increased temperature means more kinetic energy, meaning substrate molecule
entering and product leaving rates both increase. This is only valid at optimum temp of enzyme
(temp it works best at)
o Excessive heat makes atoms of enzyme move very violently, denaturing the enzyme
Cells and Cell Processes
Hypotonic Solutions – A solution with a high water potential as compared to another solution (is more
dilute (less concentrated) than another solution). If a cell is placed in a hypotonic solution it will expand
and potentially burst as water goes in it due to osmosis.
Hypertonic Solutions – A solution with a low water potential as compared to another solution (is a more
concentrated solution). If a cell is placed in this solution, it will plasmolyse (shrivel up) because water
leaves the cell via osmosis