Biology Unit 2 Topic 1+ 2 + 3 + 4

Cells

All living things are made of cells. E.g. Trees, animals etc are made of cells

Human cells (like most animal cells) consist of:

• A Nucleus - This contains the genetic material that controls activities within the cell

• A Cytoplasm - a gel-like substance containing enzymes. This is where the majority of chemical reactions occur

• A Cell Membrane - This holds the cell together and controls what substances enter and exit the cell

• Mitochondria - Most of the reactions for respiration occur within these. Respiration releases energy which is used within the cell.

• Ribosomes - Proteins are made within these

• Cell Wall - This is made of cellulose and strengthens the cell. 

• Permanent Vacuole - This contains cell sap which is a weak solution of sugar and salts

• Chloroplasts - These are where photosynthesis occurs. The contain Chlorophyll.

Diffusion:
Ecosystems

Plant Cells (usually) contain all the the things that animal cells contain, but with a few extra things:

Some organisms are single-celled like Yeast for example. A yeast cell has a nucleus, cytoplasm, and a cell membrane which is also surrounded by a cell wall.

Some cells don't have a nucleus. Bacteria are an example of this, they are a single-celled micro-organism but do not have a nucleus. Instead the genetic material is contained within the cytoplasm.

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. For example you can smell something on the other side of a room because the particles coming from that object diffuse from an area of high concentration (around the object) to an area of low concentration (around you).

Diffusion occurs within cells, substances diffuse through the cell membrane so they can be utilized within the cell. The cell membrane only lets small particles through however, so large particles such as starch have to be broken down into smaller substances like glucose before they can pass through.

An example of diffusion within cells is the movement of oxygen from the bloodstream (The area of high concentration) to the cells (an area of low concentration) for use in respiration.

With a bigger difference in concentration, the rate of diffusion is faster.

In the lungs, blood takes in oxygen from the alveolar which has a higher oxygen concentration than the blood. The circulation then takes the oxygen rich blood away and

Cell membranes

Diffusion occur at cell membranes, dissolved substances such as sugar and amino acid can move in and out of cells by diffusion.

Larger, insoluble substances such as starch, protein and fat cannot go past the cell membrane.

Particles move randomly, they move both ways but there is a net movement to one side

Specialised Cells

Palisade cells are adapted for photosynthesis

They  contain a lot of chloroplasts which increases photosynthesis

They are tall so they have a lot of surface exposed for absorbing CO2 from below

They are thin so many can be fit under the upper epidermis

Guard cells are adapted to open and close pores which controls gas exchange and water loss

They are kidney shaped which opens and closes stomata in the leaf

The stomata closes when the plant has a lot of water, as they fill up with water and become turgid making the pores open for exchanging gases

When the plant is short on water, they close as they lose water and become flaccid

They have thin outer walls and thick inner walls which allow this to work

They close at night as they are also sensitive to light, this saves water.

Red blood cells are adapted to carry oxygen

They have a concave shape which increases the surface area for absorbing oxygen

They contain a lot of haemoglobin which absorbs oxygen

They have no nucleus to leave more space for haemoglobin

Sperm cell are specilised for reproduction

They have a streamlined head with a tail ehich allows it to swim faster

It contains alot of mitochondria which help provide the energy needed

They have enzymes in their head to digest through the cell membrain of he egg

When it fuses with the egg, the cell membrane of the egg changes the structure of the cell membrane with stops  more sperm getting in and ensures the offspring has the right amount of DNA 

Egg cells contain huge food reserves which is used to feed the embryo

Differentiation occurs during the development of a multicellular organism

It is the process where cells become specialized for a particular job 

Specialised cells form tissues which forms organs which forms organ systems

Similar cells work together to form tissues

Examples are

Muscular tissues

Glandular tissues

Epithelial tissue

Organs are groups of different tissues

Organs form an organ system e.g the digestive system

Plant Structure

Plants are made of organs

These are the stems, roots and leaves, etc.

Organs are made from tissue.

Mesophyll tissues are where photosynthesis mostly occur

Xylem and Phloem transport water, mineral ions and sugar (sucrose) around the plant

Epidermal tissue covers the plant

Carbon Dioxide + water > glucose + oxygen

Photosynthesis happens in the chloroplasts of plant cells

Chloroplasts contain chlorophyll which absorbs sunlight

Photosynthesis happens in leaves

Leaves have different layers

Waxy cuticle

Upper epidermis

Palisade layer

Spongy layer

Lower epidermis

Limiting factors which affect photosynthesis

Light

Temperature

Water

Nutrient

Carbon dioxide

Greenhouses
Use of artificial light can allow photosynthesis to happen a night
Artificial heating allow photosynthesis to be at an increased rate
Additional carbon dioxide also allow photosynthesis to be at an increased rate.
These costs money but it also increases crop yield which would outweigh the cost
They would need to find the optimum condition for cost.
Paraffin lamps generates heat as well as light and carbondioxide

Glucose

Plants use glucose for many things

Respiration which releases energy which is used to convert other glucose into useful substances

Glucose can be converted to cellulose to make cell walls

Protein can be made by reacting glucose with nitrate ions absorbed from the soil

They can be stored as Starch or Fats
Starch is insoluble so it can be stored until needed
Sugar can be turned to lipids for storing in seeds

Distribution of organisms

Physical factors
Temperature
Amount of light
Availability of water
Availability of nutrients
Availability of oxygen and carbon dioxide

Environment All the conditions that surround a living organism
Habitat A place where organisms live
Population The amount of a single species in a habitat
Community The total of different organisms that live together in the habitat
Ecosystem A community and the habitat.

Transect - a line across a habitat or part of one.
Organisms are observed and recorded at regular intervals along the transect
Quadrats - a square grid, placed randomly ( gridding the area and using a random generator to find coordinates )