Cell Basics

 

   

Cell Basics

Cell Transport

Photosynthesis

Cell Respiration

Cell Division

Vocabulary: axon, ATP, cell, cell membrane, cell theory, cell wall, chloroplast, circulation, contractile vacuole, coordination, cyton, digestion, dendrite, DNA, dynamic equilibrium, endoplasmic reticulum, enzymes, eukaryotic, excretion, food vacuole, homeostasis, hormones, immunity, life processes, locomotion,  mitochondrion, movement, nucleus, neurotransmitter, organ system, organs, organelles, progesterone, prokaryotic, receptor molecules, reproduction, respiration, ribosome, synthesis, system, target cell, target organs, terminal branches, tissue

Living VS. Non-Living
Complex organisms, such as humans, require many systems for their life processes. Less complex living things may lack the complex systems of more complex organisms, but they still carry on the basic life activities. While non-living things may carry on some of these life processes, they do not carry on all of them, or these activities do not interact in a manner allowing the non-living thing to reproduce itself.

Living things carry out almost all the life processes or activities. These life processes include digestion, respiration, circulation, excretion, locomotion, immunity, coordination, and synthesis. Non-living things are incapable of carrying out at least one or more of the life processes. The sum of the energy used in all the life processes represents the metabolism of the organism. 

Homeostasis
The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or homeostasis with their surroundings. Homeostasis is a state of balance or steady state between a living thing and its environment.   Homeostasis in an organism is constantly threatened. Failure to respond effectively to a failure of homeostasis can result in disease or death. 

The components of living things in humans and other organisms, from organ systems to cell organelles, interact to maintain a balanced internal environment. This balanced internal environment is called dynamic equilibrium or homeostasis. To successfully accomplish this, organisms possess many control mechanisms that detect internal changes and correct them to restore the internal balance of the organism. If an organism fails to maintain homeostasis, this may result in disease or death. Non-living things possess few control mechanisms to maintain homeostasis.

Organizational Levels
Important levels of organization for structure and function of living things include cells, tissues, organs, organ systems, and whole organisms. The organs and systems of the body help to provide all the cells with their basic needs to carry on the life functions. The cells of the body are of different kinds and are grouped in ways that help their function.

All living things are composed of one or more cells, each capable of carrying out the life functions. The organelles present in single-celled organisms often act in the same manner as the tissues and systems found in many celled organisms. Single-celled organisms perform all of the life processes needed to maintain homeostasis, by using specialized cell organelles.

Living things have different levels of organization. The simplest level of organization is that of the cell. A group of cells with a similar function is called a tissue. Groups of tissues working together to perform a common function are called organs. An example of this would include the nervous, muscle, and other tissues which make up the heart.   Groups of organs working together to perform a common function are referred to as a system or organ system.   The blood vessels, blood, and the heart are organs which work together to form the circulatory system. Many different systems function together to allow a complex organism to function.

Cell Structure
Cells have particular structures or organelles that perform specific jobs. These structures perform the life activities within the cell. Just as body systems are coordinated and work together in complex organisms, the cells making up those systems must also be coordinated and organized in a cooperative manner so they can function efficiently together.

Inside the cell a variety of cell organelles, formed from many different molecules, carry out the transport of materials, energy capture and release, protein building, waste disposal, and information storage. Each cell is covered by a membrane that performs a number of important functions for the cell as well.

Cell Theory
All organisms contain one or more cells which are capable of carrying on the life activities needed by the organism. This idea is often referred to as the cell theory.

Parts of the Cell Theory

  • The cell is the unit of structure in all living things.
  • The cell is the unit of function in all living things.
  • All cells come from preexisting cells.

A few exceptions to this theory exist. Viruses lack typical cellular structure. There also is some question as to how the the first cell arose. In general, the cell theory holds true for most living things, however.

Cell Types
There are two distinct types of cells. Prokaryotic cells lack a nucleus and other organelles. Two domains of organisms have this type of cell - Archaebacteria and Eubacteria, the simplist of all organisms. They still perform life functions but all activities must be accomplished in the cytoplasm. Eukarotic cells are found in organisms from the domain Eukarya, which includes all protists (Ameoba and Paramecium are examples), Fungi (yeast and mushrooms are examples), Plants (mosses, ferns, gymnosperm pines and angiosperm flowering plants are examples), and Animals (humans are examples).

Figure 2.  The cells of eukaryotes and prokaryotes

 

Cell Organelles
Cells have particular structures that perform specific jobs. These cell structures are called organelles and perform the actual work of the cell. These organelles are formed from many different molecules. Some functions carried out by organelles include the transport of materials, energy capture and release, protein building, waste disposal, and information storage. Single celled organisms also have organelles similar to those in more advanced organisms to complete their life processes. Many enzymes are needed for the chemical reactions involved in cellular life processes to occur.

A Typical Animal Cell

 

Some Cell Organelles

Cell Organelle

Function

nucleus control center of the cell

contains DNA which directs the synthesis of proteins by the cell

mitochondrion carries on the process of cell respiration converting glucose to ATP energy the cell can use
endoplasmic reticulum transport channels within the cell
ribosome found on the endoplasmic reticulum and free within the cell 

responsible for the synthesis of proteins for the cell

cell membrane selectively regulates the materials moving to and from the cell
food vacuole stores and digests food
contractile vacuole found in many single celled aquatic organisms

pumps out wastes and excess water from the cell

chloroplast found in plant cells and algae 

carries on the process of photosynthesis

cell wall surrounds and supports plant cells

  Life Functions
Humans and many other organisms require multiple systems for digestion, respiration, reproduction, circulation, excretion, movement, coordination, and immunity. The systems collectively perform the life processes.  

Once nutrients enter a cell, the cell will use those raw materials for energy or as building blocks in the synthesis of compounds necessary for life.  The energy we initially obtain must must be changed into a form cells can use. A type of protein called an enzyme allows for these changes to occur within the cell.

Humans and other complex organisms require many different organ systems to carry on the activities required for life. These life activities or processes include digestion, respiration, reproduction, circulation, excretion, movement, coordination, and immunity.  

Life Processes

Digestion breakdown of food to simpler molecules which can enter the cells
Circulation the movement of materials within an organism or its cells
Movement (locomotion) change in position by a living thing
Excretion removal of cellular waste products by an organism (wastes may include carbon dioxide, water, salt, and urea and are released during exhalation, perspiration, and urine formation.)
Respiration process which converts the energy in food to ATP (the form of energy which can be used by the cells)
Reproduction the making of more organisms of one's own kind -- not needed by an individual living thing but is needed by its species
Immunity the ability of an organism to resist disease causing organisms (pathogens) and foreign invaders
Coordination the control of the various activities of an organism (mostly involves the nervous system and endocrine glands in complex animals)
Synthesis the production of more complex substances by combining two or more simpler substances

It is important to realize that cell organelles are involved in many of these life processes, as well as the organ systems of complex organisms.

Cellular Communication
Neurotransmitters
and hormones allow communication between nerve cells and other body cells as well. If nerve or hormone signals are changed, this disrupts communication between cells and will adversely effect organism homeostasis. Additionally, the DNA molecule contains the instructions that direct the cellís behavior through the synthesis of proteins.

Cell Membrane Receptors

Cell Membrane Receptors

Many cell membranes have receptor molecules on their surface. These receptor sites play an important role in allowing cells and organs to communicate with one another.

Hormonal Regulation
Hormones provide a primary way for cells to communicate with each other. A hormone is a chemical messenger with a specific shape that travels through the bloodstream influencing another target cell or target organ. Upon reaching the cell the hormone is targeted for, the hormone often activates a gene within a cell to make another necessary compound. One example of this is provided by the pituitary gland. This gland at the base of the brain makes a hormone called LH (luteinizing hormone). This hormone travels through the bloodstream and stimulates the ovary to produce yellow tissue that produces the hormone progesterone, which maintains the thickness of the uterus lining. The graphic below illustrates how this kind of hormonal regulation can work in a plant cell. Animal cell hormonal regulation involves a similar mechanism.

A Hormonal Feedback Mechanism 

The diagram at the right illustrates how a hormone can bind to receptors on a cell membrane and trigger that cell to produce a needed compound.

Nervous Regulation
Nerve cells or neurons also allow cells to communicate with each other. Neuron communications are one way organism can detect and respond to stimuli at both the cellular and organism level. This detection and response to stimuli helps to maintain homeostasis in the cell or organism. Neurons may stimulate other nerve cells or muscle cells, thus causing the later to contract and produce movement.

Structure and Function of a (Neuron) Nerve Cell

Structures and their Functions

1.   dendrite -- neuron branch which detects stimuli (changes in the environment)

2.  cyton -- cell body of the neuron where normal metabolic activities occur

3.  axon -- longest dendrite covered by a myelin sheath which provides electrical insulation -- carries nerve message or impulse to the terminal branches

4.  terminal branches -- release nerve chemicals called neurotransmitters which stimulate adjacent dendrites on the next neuron or a muscle cell

Any change in nerve or hormone signals will change the communication between cells and organs in an organism and thus may cause problems for organismís stability and ability to maintain homeostasis.

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