Animal (human) cell - This cell contains the nucleus, this contains the DNA that control the activities of the cell. It also contains the cytoplasm this is a gel-like substane where most of the chemical reaction takes place. The cell membrane holds the cell together and controls what goes in and out. The mitocondria where the energy from respiration is released. Finally, the ribosomes are where proteins are made in the cell.
Plant cells - These cells have all these parts but have a few extra. For example, the cell wall strengthens the cell. The permanent vacuole contains cell sap and chloroplasts absorb light energy and makes foods for the plant.
Yeast cells - Yeast have only one cell. They have the cell wall, nucleus, cell membrane and cytoplasm.
Bacterial cells - Bacterial cell doesnt a nucleus so the DNA floats in the cytoplasm. This cells contains cell membrane and cell wall.
Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration. This only happenings in solutions and gases. For example, the smell of perfume diffuses through the air in a room. The bigger the difference in concentration, the faster the rate of diffusion.
Cell membranes hold the cell together but they also let stuff in and out. dissolved substances can move in and out of cells by diffusion. Only very small molecules can fit through the cell membrane, e.g. oxygen, glucose and amino acids. The molecules moves from a high concentraction to low concentration.
specialised cells and tissues
Specialised cells are cells that carry out a specific function. They have special features that help them to carry out this function. For example, palisade leaf cells carry out lots of photosynthesis. They contain lots of chloroplasts, which are needed for photosynthesis.
The process by which a cell changes to become specialised is called differentiation. Differentiation occurs as a multicellular organism developes. Specialised cells form tissues, which form organs, which form organ systems. Large multicellular organisms have different systems inside them for exchanging and transporting materials.
A tissue is a group of similar cells that work together to carry out a particular function. In mammals, tissues include:
- Muscular tissue, which contracts to move whatever its attached to.
- Glandular tissue, which makes substances like enzymes and hormones
- Epithelial tissue, which covers some parts of the body, e.g. the inside of the gut.
organs and organ systems
An organ is a group of different tissues that work together to preform a certain function. The stomach is an organ made of these tissues:
- Muscular tissue, which moves the stomach wall to churn up the food.
- Glandular tissue, which makes digestive juices to digest food
- Epithelial tissue, which covers the outside and inside of the stomach.
An organ system is a group or argans working together to preform a particular function. The digestive system is found in humans and other mammals. The digestive system breaks down food. It does this by releasing digestive juices. Then the digestve systems abosrbs the products of digestion.
Plant structure and photosynthesis
Plants are made of organs like stems, roots and leaves. Leaves are made of these tissues:
- Epidermal tissue covers the whole plant.
- Mesophyll tissue is where most of the photosynthesis in a plant occurs.
- Xylem and phloem vessels transport substances around the plant.
Photosynthesis is the process that makes glucose in the plants and algae .Photosynthesis happens inside the chloroplasts. Chloroplasts contain a green substance called chlorophyll. Chlorophyll absorbs energy from sunlight. The energy is used to turn carbon dioxide and water into glucose. Oxygen is also made as a by product
CARBON DIOXIDE + WATER --------------------> GLUCOSE + OXYGEN.
The rate of photosynthesis
The rate of photosynthesis depends on:
- how much light there is,
- the amount of carbon dioxide
- the temperature
Any of these three factors can become the limiting factor. A limiting factor is something that stops phtoosynthesis from going any faster. For example:
- At night, light is the limiting factor
- In winter, its often temperature thats the limiting factor.
- If its warm enough and bright enough then carbom dioxide is the limiting factor.
Greenhouses are made out of glass so they let a lot of loght through. Farmers can also supply plants with artificial light at night. This means photosynthesis can carry on at night. Farmers can also add more carbon dioxide by using paraffin heater that makes carbon dioxide as it burns. Greenhouses are warm because they trap the sun's heat In winter, farmers can use a heater to keep everything warm. In summmer, they open the windows or uses shades to cool everyhting down.
Giving plants more light, carbon dioxide and heat costs money. If the farmer keeps everything just right then the plants grow faster. This means more crop and then more money.
How plants use glucose
For respiration, plants make glucose in their leaves. They then use some some the glucose for respiration.
Making cell walls, glucose is made into cellulose. Cellulose is used to make strong cell walls.
Making proteins, plants absorb nitrate ions from the soil. Gluose is joined with nitrate ions to make amino acids. The amino acids are then made into proteins.
Stored in seeds, Glucose is turned inot fats and oils for storing in seedds. For example, we get margarine from sunflower seeds. Seeds also store starch.
Stores as starch, Glucoseis turned into starch and stored in roots, stems and leaves. For example, potato and parsnip plants store starch - we eat the swollen torage organs. Starch is insoluble - i doesnt dissolve. This makes starch much better for storing than glucose.
Distribution of oranisms
The distribustion of an organism is where an organism is found. Where an organism is found is affected by enviromental factors, such as: the temperature, how much water, amount of light, how much oxygen and carbon dioxide and if there are enough nutrients. An organism might be more common in one area than another due to differences in enviromental factors between the two areas. For example, in f field, you might find that daisies are more common in the open than under trees, because there's more light. To study the distribution of an organism you can use quadrats or transects.
You can see how common on organism is in two different areas - these are called sample areas. Place a 1m2 quadrat on the ground at a random point withing the first sample area, e.g. divide the area into a grid and use random number tables to pick coordintes. Count all the organisms withing the quadrat. Repeat steps 1 and 2 as many times as you can. Work out the mean, median, mode. Fpr example, 7 quadrats are 5, 6, 7, 7, 7 ,9. Mean is total number (49) divided by number of quadrates (7) which is 7 daises per quadrat. The mode is 7 and the median is 7. Repeat steps 1 tp 4 in the second sample area. Compare the two means.
Populaion size = mean number of organisms per 1m2 quadrat x total area (m2). For example. there are 7 daises per m2 in a 100m2 field. So the population size is 7 x 100 = 700 daisies.