Cells

Cells are considered the basic units of life in part because they come in discrete and easily recognizable packages. That's because all cells are surrounded by a structure called the cell membrane.

The cell is the very smallest unit of living matter. All living things including plants and animals are made up of cells. Cells are made of atoms, which are the smallest units of matter. There are many different kinds of cells. The two kinds you are most likely to be familiar with are animal and plant cells. Some of the differences between them are that plant cells have a cell wall and chloroplasts.
Cells all have different sizes, shapes, and jobs to do.
The cells in a single organism may have different shapes, sizes, and jobs. Organisms like humans are made up of trillions of cells. There are also one-celled organisms such as euglenas, amoebas, and bacteria. Two-thirds of a cell is water, which means that two-thirds of your whole body is water. The rest is a mixture of molecules, mainly proteins, lipids and carbohydrates. Your cells turn the raw materials in the food you eat into the molecules your body needs, using thousands of different chemical reactions.

In our body there are many different kinds of cells. We are made up of about 200 different types of cells. Our body also has non- living materials such as hair, fingernails, and the hard part of the bone and teeth. All these materials are made up of dead cells.

All cells have some parts in common. One part found in all cells is the cell membrane. The cell membrane surrounds the cell, holds the other parts of the cell in place, and protects the cell. Molecules can pass in and out of the cell membrane. Inside the membrane, all cells, except for bacterial cells, contain a nucleus and cytoplasm. The nucleus is a dark structure located in the middle of the cell. It controls the cell's activities, and acts like the cell's brain. Inside the nucleus there is DNA, which contains genetic information. The cytoplasm is a jelly-like substance inside the cell where most of the cell's activities take place. It's made out of water and other chemicals. All cell parts, except the nucleus, are located in the cytoplasm.

Each cell was made from an already existing cell. New cells are made through a process called cell division or mitosis. One cell turns into two cells and then two cells turn into four cells, etc. Even humans started life with only one cell. Most of the cells in many celled-organisms use mitosis to reproduce. The basic steps in mitosis are:
1) The start of mitosis chromosomes is in the nucleus.
2) The chromosomes in the nucleus will then make a copy of themselves
3) Next the cell divides.
4) Last one set of chromosomes goes to the new cell and one set remains in the parent cell.

*The cell is compose by different thing

Nucleus
- Large Oval body near the center of the cell.
- The control center for all activity.
- Surrounded by a nuclear membrane.

Nucleoplasm
- Is the protoplasm in the nucleus.
- Contains genetic material ---> CHROMOSOMES (DNA)

Nucleolus
- Is found in the nucleus.
- Contains more genetic information (RNA)

Cell Membrane
- The outer boundary of the cell.
- It separates the cell from other cells.
- It is porous ---> allows molecules to pass through.

Cell Wall (Plant Cells Only)
- Non-living structure that surrounds the plant cell.
- Protects + supports the cell.
- Made up of a tough fiber called cellulose.

Cyto Plasm
- Cell material outside the nucleus but within the cell membrane.
- Clear thick fluid.
- Contains structures called organelles.

Vacuoles
- Are clear fluid sacs that act as storage areas for food, minerals, and waste.
- In plant cell the vacuoles are large and mostly filled with water. This gives the plant support.
- In animal cells the vacuoles are much smaller.

Mitochondria
- Powerhouse of the cell.
- Center of respiration of the cell.
- They release energy for cell functions.

Chloro Plasts (Plant cells only)
- Contains a green pigment known as chlorophyll, which is important for photosynthesis.

Ribosomes
- Tiny spherical bodies that help make proteins.
- Found in the cyto plasm or attached to the endo plasmic reticulum.

Endo Plasmic Reticulum (ER)
- Systems of membranes throughout the cyto plasm.
- it connects the nuclear membrane to the cell membrane.
- Passageway for material moving though the cell.

Golgi Bodies
- Tube like structures that have tiny sacs at their ends.
- They help package protein.

Lysosomes
- " Suicide sacs "
- Small structures that contain enzymes, which are used in digestion.
- If a lysosome were to burst it could destroy the cell.

There are two main groups of cells, prokaryotic and eukaryotic cells. They differ not only in their appearance but also in their structure, reproduction, and metabolism. However, all of the cells belong to one of the five life kingdoms. The greatest difference lies between cells of different kingdoms. The following diagram shows the five kingdoms: monera, protista, plantae, fungi, and animalia.

*Prokaryotic Cells
Cells that lack a membrane-bound nucleus are called prokaryotes. These cells have few internal structures that are distinguishable under a microscope. Cells in the monera kingdom such as bacteria and cyanobacteria are prokaryotes.
Prokaryotic cells differ significantly from eukaryotic cells. They don't have a membrane-bound nucleus and instead of having chromosomal DNA, their genetic information is in a circular loop called a plasmid. Bacterial cells are very small, roughly the size of an animal mitochondrion. Prokaryotic cells feature three major shapes: rod shaped, spherical, and spiral. Instead of going through elaborate replication processes like eukaryotes, bacterial cells divide by binary fission.

*Eukaryotic cells
Eukaryotic cells comprise all of the life kingdoms except monera. They can be easily distinguished through a membrane-bound nucleus.
Eukaryotic cells also contain many internal membrane-bound structures called organelles. These organelles such as the mitochondrion or chloroplast serve to perform metabolic functions and energy conversion. Other organelles like intracellular filaments provide structural support and cellular motility. The function of individual organelles is described in detail in the Cell Anatomy Section.
Another important member of the eukaryote family is the plant cell. They function essentially in the same manner as other eukaryotic cells, but there are three unique structures, which set them apart. Plastids, cell walls, and vacuoles are present only in plant cells.

Bacteria perform many important functions on earth. They serve as decomposers, agents of fermentation, and play an important role in our own digestive system. Also, bacteria are involved in many nutrient cycles such as the nitrogen cycle, which restores nitrate into the soil for plants. Unlike eukaryotic cells that depend on oxygen for their metabolism, prokaryotic cells enjoy a diverse array of metabolic functions. For example, some bacteria use sulfur instead of oxygen in their metabolism.

Universidad Regiomontana
Chepevera Campus

Biology class

The Cell

Cecilia Gabriela Saavedra Corona

710963

24/01/14