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Biology AQA GCSE Unit 2
Transcript of Biology AQA GCSE Unit 2
Cells are the smallest unit of life. All living things are made up of cells.
Most human cells, like most other animal cells, have the following parts:
> Nucleus - controls the activity of the cell
> Cytoplasm - where most of the chemical reactions take place
> Cell Membrane - controls the passage of substances in and out of the cell
> Mitochondria - where most energy is released during respiration
> Ribosomes - where protein synthesis occurs
Solely in plant and algal cells:
> Cell Wall - made of cellulose and strengthens plant cells
> Chloroplasts - absorb light energy to make food in plant cells
> Permanent Vacuole - filled with cell sap in plant cells > Large multicellular organisms develop systems for exchanging materials
> During the development of a multicellular organism, cells differentiate so that they can perform different functions
> A tissue is a group of cells with similar structure and function
> Organs are made of tissues
> One organ may contain several tissues
> Organ systems are groups of organs that perform a particular function. The cells of multicellular organisms may differentiate and become adapted for specific functions. Tissues are aggregations of similar cells; organs are aggregations of tissues performing specific physiological functions. Organs are organised into organ systems, which work together to form organisms. Plant organs include stems, roots and leaves. Examples of plant tissues include:
> Epidermal tissues, which cover the plant
> Mesophyll, which carries out photosynthesis
> Xylem and phloem, which transport substances around the plant Examples of animal tissues include:
> Muscular tissue, which can contract to bring about movement
> Glandular tissue, which can produce substances such as enzymes and hormones
> Epithelial tissue, which covers some parts of the body
Photo = Light
Synthesis = making of (glucose)
Photosynthesis = making glucose using light
> Farmers artificially manipulate the environment in which they grow plants.
> They grow plants in greenhouses or in polythene tunnels
> They can control the temperature in greenhouses using heaters and ventilation
> They can artificially increase the carbon dioxide levels
> They can control the light using fluorescent lamps
> By doing all of this, their plants grow faster and certain plants can be grown in the UK out of their natural growth season e.g. tomatoes.
> This allows farmers to maximise their profits 1) Temperature - A low temperature will limit the rate as the molecules will move less and therefore the reaction will happen slower
2) Carbon Dioxide - A shortage of CO2 will limit the rate because fewer molecules will be available for the reaction
3) Light Intensity - A shortage of light means there is less energy to power the reaction.
Movement in & out of cells Yeast
> Yeast is a single-celled organism
> The cells have a nucleus, cytoplasm, and a membrane surrounded by a cell wall
> Bacterium is a single celled organism
> A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall
> The genes are not in a distinct nucleus
> Cells may be specialised to carry out a particular function > To get into or out of cells, dissolved substances have to cross the cell membranes
> Solutes = particles in solution, e.g. glucose, sodium ions
> Solvent = liquid in which the particles are dissolved e.g. water
> Solute and solvent molecules move around randomly
> Solutes can move into and out of cells by diffusion Diffusion > Diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they of a higher concentration
> Oxygen required for respiration passes through cell membranes by diffusion
> The greater the difference in concentration, the faster the rate of diffusion The stomach is an organ that contains:
> Muscular tissue, to churn the contents
> Glandular tissue, to produce digestive juices
> Epithelial tissue, to cover the outside and inside of the stomach The digestive system is one example of a system in which humans and other mammals exchange substances with the environment.
The digestive system includes:
> Glands, such as the pancreas and salivary glands, which produce digestive juices.
> The stomach and small intestine, where digestion occurs
> The liver, which produces bile
> The small intestine, where the absorption of soluble food occurs
> The large intestine, where water is absorbed from the undigested food, producing faeces During photosynthesis:
> Light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some cells and algae
> This energy is used by converting carbon dioxide (from the air) and water (from the soil) into sugar (glucose) Carbon Dioxide + Water ---(Light energy)--> Glucose + Oxygen Where does photosynthesis happen?
> Leaves are the main site of photosynthesis
> Photosynthesis mainly occurs in the mesophyll cells
> These cells contain lots of chloroplasts
> Chloroplasts contain chlorophyll With no limiting factors, increasing a factor above a certain level will not increase the rate. All chlorophyll molecules are being used. How do plants and algae use glucose? > The glucose produced in photosynthesis may be converted into insoluble starch for storage
> Plant cells use some of the glucose produced during photosynthesis for respiration
> Some glucose in plants and algae is used:
> to produce fat or oil for storage
> to produce cellulose, which strengthens the cell wall
> to produce proteins (plants also use nitrate ions
that are absorbed from the soil