B2

CELLS

B2.1

Cells - The basic unit structure in all organisms.

  • ‘Building blocks of life’ (smallest unit)

  • Capable of surviving on their own.

  • Can replicate independantly.

Multicellular organism - Composed of many cells.

Unicellular organism - Composed of only one cell (Bacteria)

How are new cells made?

In multicellular organisms, new cells are made by splitting into 2. The 2 new cells can then split into 4 cells and so on. When they do this, they are either growing or replacing dead cells.

In unicellular organisms, each individual cell is an organism. When a cell divides into 2, it is reproducing. This is called assexual reproduction.

Eukaryotic and Prokaryotic Cells

Plant and Animal Cells → Eukaryotes

  • Have a nucleus

Bacteria Cells → Prokaryotes

  • Do not have a nucleus

Hierarchy

Cell → Tissue → Organ → Organ System → Organism

Tissue

Group of cells working together for a specific function

Organ

Group of tissues working together for a particular function

Organ system

Group of organs working together for a major function

Organism

An individual living being that can carry out all life processes, made up of one or more cells.

Cell structure

Three types of cells

  • Plant

  • Animal

  • Bacterial

Plant Cell

Plant cell → Eukaryotic → Multicellular organisms

(They have all components of an animal cell and a few others)

Plant Cell

Parts and Functions-

Cell wall

  • Strengthens the cell and gives it support.

  • Made of cellulose

Cell membrane

  • Controls the movement of substances in and out of the cell.

Nucleus

  • Contains the plant’s genetic material

    (DNA = instructions for making new cells)

Permanent Vacuole

  • Stores nutrients in the form of sap, and water and waste products.

  • Keeps cell structure rigid to support the plant.

Cytoplasm

  • Liquid - gel structure where chemical reactions take place.

  • It is where all the organelles are suspended.

Mitochondria

  • Provide cells with energy during respiration.

Chloroplast

  • Contains chlorophyll → green pigment which absorb sunlight for photosynthesis.

  • It is where photosynthesis happens.

Ribosomes

  • Synthesise proteins from amino acids.

Animal Cell

Animal Cell → Eukaryotic → Multicellular organisms

Animal Cell

Parts and Functions-

Nucleus

  • Contains the animal’s genetic material

    (DNA = instructions for making new cells)

Cytoplasm

  • Liquid - gel structure where chemical reactions take place.

  • It is where all the organelles are suspended.

Cell membrane

  • Controls the movement of substances in and out of the cell.

Mitochondria

  • Provide cells with energy during respiration.

Ribosomes

  • Synthesise proteins from amino acids.

Plant cell vs Animal cell

Animal cells have all of the same structures as plant cells, except the following:

Cell membrane, permanent vacuole, chloroplasts. (because they do not need them)

Bacterial Cell

Bacteria cell → Prokaryotic cell → Unicellular organisms

Bacteria Cell

Parts and Functions:

Circular DNA (strands)

  • Genes they need to survive and reproduce (instead of a nucleus)

  • One circular, strand

  • Free to float around the cytoplasm

Plasmid

  • Carry ‘extra’ genes such as antibiotic resistance

  • Only some bacterial cells have them

Flagellum

  • Thread like structures that portrude from the back of the cell.

  • Allow the bacteria to move around freely.

  • The bacteria will move towards beneficial substances (nutrients/oxygen) and away from harmful substances (toxins).

Cell wall

  • Strengthens the cell and gives it support.

  • Made of cellulose

Cell membrane

  • Controls the movement of substances in and out of the cell.

Cytoplasm

  • Liquid - gel structure where chemical reactions take place.

  • It is where all the organelles are suspended.

Ribosomes

  • Synthesise proteins from amino acids.

Common Features of the 3 cell types

Specialised cells

In addition to the basic cell, organisms have many specialised cells that perform specific functions.

Cilliated Cell

Controls the movement of mucus in the trachea and bronchi.

  • They line the surfaces of respitory passages.

  • They have hair like portrusions that move rythmically to push mucus towards the nose and mouth where it can be removed.

  • The mucus is created by goblet cells, which are dotted in between ciliated cells.

  • The mucus captures particles such as pathogens, bacteria and viruses so they cannot enter the lungs.

Cilliated Cell

Root hair Cell

Aids the absorption of water and mineral ions from the soil.

  • Located at the edge of the roots close to the soil.

  • Have long potrutions to increase the surface area and increase the absorption rate.

  • Thin, permeable cell wall.

  • Water enters by osmosis and minerals through active transport.

  • Have lots of mitochondria to provide energy during active transport.

B2.2

Size of Specimens

Images we use to observe cells have all been magnified. Real life cells can only be seen under a microscope.

The following formula indicates by how much an image has been magnified:

Magnification = Image size/Actual size

Units: Both Image size and Actual size must be in mm

  • Remeber to check the units and then convert them before calculating!

Example:

An image of a leaf is 30mm in size and it’s actual thickness is 2mm. What is the maginification?

30mm ÷ 2mm = 15mm

Answer = 15 (no units)

How to convert micrometers into milimeters

Micrometers = µm

From µm → mm = divide by 1000

From mm → µm = multiply by 1000