7th Grade Life Science

Cell Biology: Viruses and Cells

Virus- is it a living organism?

a. Structure-

1. it has hereditary material inside

2. covered or surrounded by a protein sheath or coat

3. introduces or injects its hereditary material into other cells through tail

4.they are classified by shape, the type of organism they infect, the way they reproduce, or the type of hereditary material they carry

 

b. Reproduction-

1. viruses use hereditary material land "machinery" from other living cells to reproduce- they may damage or destroy the host cell in the process.

Viruses can invade organisms by way of the air, food, water, body fluids, or through an insect (known as an intermediate host). Once they enter the host they can either become active or latent (inactive/a resting stage)

Active Virus-

1.attaches to a cell and injects their hereditary material inside

2. the viral hereditary material then takes over and controls the host’s cell hereditary material- instructs it to make more viruses.

3. Hundreds of new viruses (virus particles) cause the cell to burst thus releasing the viruses to infect new cells. Host cell dies in the process.

4. Examples: small pox, measles, flu, colds, HIV

 

This cycle of infection and release occurs in the host organism until the organism either destroys the virus or dies from the infection.

Latent Virus-

1.attaches to a cell and injects their hereditary material inside

2. the viral hereditary material becomes part of the host’s cell hereditary material-but does not take over control of the host for a period of time (latent)

3. the period of latency varies depending on the type of virus, the host organism, and other conditions.

4. when the period of latency ends it becomes active (follows the same steps as an active one).

5. Examples: cold sore

Viruses cause disease or death in all types of organisms- because of the way it reproduces.

Vaccines are developed by taking damaged viruses and injecting them into the organism. The organism then develops antibodies to attack either the damaged or the undamaged viruses.

Some viruses are helpful

1. they can be tricked into placing good genes into defective cells- gene therapy

2. some viruses attack "pests"

2.3 Cells: The Unit of Life

Cell Theory:

1. all organisms are made up of one or more organisms

2. cells are basic unit of structure and function in all organisms

3. all cells come from cells that already exist

Cells- the smallest units that carry out the life processes of an organism. Most are microscopic

Cell Structure: each cell is composed of smaller parts (called organelles) which carry out the activities of the cell.

Two general types of cells:

Procaryotic-most primitive, have no organized nucleus, it is no membrane around its hereditary material

Eucaryotic-more advance, has an organized nucleus, it has a membrane around its hereditary material

1. Cell Membrane: forms the boundary of the cell:

Functions: 1. Traffic controller- controls what enters and leaves the cell

(food, water, oxygen in and wastes out)

2. Provides shape and structure for the cell.

2. Cytoplasm-gel-like substance inside the cell membrane, the organelles are contained in it

Functions: Contains the raw materials necessary for the chemical activities of the cell- proteins, lipids, carbohydrates, water, oxygen)

3. Nucleus- largest organelle in the cell, controls all cell activities,

a. Contains genetic blueprints or codes in chromatin (long strands of protein and DNA (a nucleic acid)

b. contains a nucleolus that controls the making of proteins in the cell.

 

4. Organelles-

a. endoplasmic reticulum-transportation system within the cell

b. ribosomes- are the site of protein manufacture

c. golgi bodies-move proteins outside the cell

d. mitochondria- site of cellular respiration, where oxygen is added to

food (glucose) to make usable energy

e. lysosome- digests wastes and worn out cell parts

f. vacuole- holds water, food, wastes,

g. vesicles- bubble-like structures which transport materials within a cell

 

Differences between Cells:

Plant Cells-have the following structures

a. Cell wall- provides structure, shape, and protection for plant cell b. Chloroplast- an organelle where photosynthesis takes place

(sun’s energy is transformed into chemical energy-glucose)

c. Vacuole-very large, provides additional structure and support for cell

	Plant	Animal	Monera	Virus
Organelles+nuc	yes	yes	no	no
Cell wall	yes	no	yes	no
Chloroplast	yes	no	no	no
Protein coat	no	no	no	yes
Hereditary material	yes	yes	yes	yes
Vacuole	1 very large	Many small	none	none

Cell Types:

a. Types of cells- shape is key, often indicates its function or purpose

b. nerve cell- up to 1m long- carries signals to and from, like a phone line

c. egg and sperm cells- for reproduction, in humans very small

d. red blood cells- very small, carries oxygen

e. white blood cells-attack foreign materials, part of the immune response

f. other types include brain, skin, muscle, bone, digestive- special shape and purpose

Cell Organization:

Tissues: similar cells grouped together to perform a particular function (ex, muscles)

Organs: different tissues grouped together to perform particular functions (ex. Liver, lungs)

System: different organs grouped together to perform particular functions (ex. Circulatory, digestive, excretory)