Name: Sect: Date:
Cells
Cell Theory
The cell theory is a widely accepted explanation of the relationship between cells and living things. The cell theory states:
· All living things are made of cells.
· New cells are created by old cells dividing into two.
· Cells are the basic building units of life.
Types of Cells
· Prokaryotic- simpler cells such as viruses and bacteria that do not have a nucleus
· Eukaryotic- more complex cells found in plants and animals that contain a nucleus
Cells Have Basic Needs
Living organisms have basic needs because their cells have basic needs. Cells, like organisms, typically need:
· water
· nutrients/food
· an environment in which they can live
· a means of removing the waste
Typical Plant Cell
Organelle / Structure / Function / Analogy
cell wall / rigid and flexible layer that surrounds and protects plant cells / Strong wall that protects a city
cell membrane / selectively permeable layer (controls what enters or leaves) / guards that control who enters or leaves
cytoplasm / gel-like fluid that fills the cell and surrounds the organelles / the space filling up the inside of the city
Organelle / Structure / Function / Analogy
nucleus / directs all of the cell’s activities; the “brain” of the cell / Town hall building which controls the city
nucleolus / found in the nucleus; produces ribosomes and proteins / Carpenters which build the workshops; their office is in the town hall
chromatin / / found in the nucleus; contain the “instructions” to run the cell / the blueprints or data base used to run the city
ribosomes / produce proteins; found floating in cytoplasm or attached to the endoplasmic reticula / workshops that produce city’s main product (widgets)
mitochondria / / site of cellular respiration; where sugars are broken down for energy / the power plant of the cell
chloroplasts / contain chlorophyll and give plants green color; where photosynthesis occurs / the solar panels that make energy from sunlight
lysosomes / / break down food or toxic molecules / the maintenance crew
golgi body / / packages the proteins made by the ribosomes to be sent to other parts of the cell / the mail room
endoplasmic reticulum / / system of passageways that move materials like proteins around the cell / the transportation system
vacuoles / storage area for food, water and waste in a cell; help plants remain ridgid / the water tower
Although some cells contain a different assortment of organelles than others, a list of the organelles commonly found in most plant and animal cells appears below:
· Cytoplasm is a gel-like fluid that fills the cell and surrounds the other organelles.
· Nucleus is like the “brain” of the cell. It contains chromosomal information on chromatin. Chromatin is composed of long, thin strands of DNA which contains “instructions” that control cell metabolism and heredity.
· Ribosomes are small grain-like bodies that produce proteins.
· Mitochondria take in nutrients, break them down during cellular respiration, and create energy for the cell.
· Chloroplasts are the food producers in a plant cell. During a process known as photosynthesis, chloroplasts absorb light energy from the Sun and produce food in the form of glucose sugar from carbon dioxide and water.
· Endoplasmic reticula transport chemicals between and within cells.
· Vacuoles store water and ingested food in a fluid sack. They also remove wastes from cells and produce turgor pressure against the cell wall for cellular support.
· Lysosomes contain enzymes specialized to break down ingested materials, secretions, and wastes.
· Golgi bodies (or Golgi apparatus) process cellular wastes and other materials and transport them out of the cell. In addition to playing an important role in waste disposal, Golgi bodies also process, sort, and modify proteins in cells.
· The cell membrane (or plasma membrane) acts as a boundary layer around the cytoplasm thus separating cells from their outside environments. In addition to being able to recognize chemical signals, the cell membrane is selectively permeable to chemicals and controls which molecules enter and leave the cell. Nutrients first enter the cell through the cell membrane.
· The cell wall is a secretion of the cell membrane. It provides protection from physical injury, and with the vacuole, it provides structural support.
Plant cells and animal cells contain different cellular structures. For example, most plant cells possess a cell wall and chloroplasts. Animal cells never contain these structures. Plant cells also always contain large vacuoles. Some animal cells also have vacuoles, but the vacuoles in animal cells are much smaller than those found in plant cells.
Photosynthesis
Plants are autotrophs, organisms that make their own food. During photosynthesis, plants use energy from the sun to convert carbon dioxide and water into oxygen and sugars. Sunlight is captured by the chloroplasts where it is absorbed by a green pigment, chlorophyll. The plant then uses two other raw materials, water (H2O) and Carbon Dioxide (CO2) to create the glucose (a type of sugar). The H2O comes from the roots through the xylem. The CO2 comes from openings on the bottom of the leaf called stomata.
Respiration
Respiration is the process by which cells produce energy from glucose. Cells break down glucose and release the energy that it contains. This process happens continuously in the mitochondria.
Fermentation
Some cells obtain their energy through fermentation, an energy releasing process that does not require oxygen. Fermentation provides
energy for cells without using oxygen. One type of fermentation occurs
in yeast and some other single-celled organisms. This process is
sometimes called alcoholic fermentation because alcohol is one of the
products made when these organisms break down sugars. Another type
of fermentation takes place at times in your body, for example, when
you’ve run as fast as you could for as long as you could. One product of
this type of fermentation is an acid known as lactic acid. When lactic acid builds up, your muscles feel weak and sore.