Cell Structure and Nucleus

Cells are an organism's smallest living units. Whatever type of cell they are, all cells share three characteristics.

All cells have:

Cell membrane, which separates the inside the cell from its environment
Cytoplasm is a jelly-like fluid that contains DNA, which is the genetic material of the cell.

Prokaryotes and Eukaryotes

There are two broad categories of cells.

Eukaryotic cells are the first category. They have organelles such as the nucleus and other unique parts. Eukaryotic cells are more complex, advanced cells found in plants and animals.
Prokaryotic cells are the second type of cell. They lack a nucleus and membrane-enclosed organelles. They have genetic material, but it is not housed within a nucleus. Prokaryotic cells, like bacteria, are always one celled or unicellular organisms.

So what are organelles?

Organelle means "small organ." Organelles are specialized parts of cells that perform specific functions. Let's start with the nucleus:

Nucleus

The nucleus is the cell's command and regulation center. DNA, or genetic material, is found in the nucleus. DNA determines what the cell will do and how it will do it.

Chromatin

Chromatin the tangled, spread out form of DNA found inside the nuclear membrane.

Chromosomes

When a cell is ready to divide DNA condenses into structures known as chromosomes.

Nucleolus

The nucleus also contains a nucleolus, which is a structure where ribosomes are made.

Ribosomes

After ribosomes leave the nucleus they will have the important job of "synthesizing", or making proteins.

Cytoplasm

Outside the nucleus the ribosomes and the rest of the organelles float around in cytoplasm, which is the jelly-like substance.

Endoplasmic Reticulum ER

Ribosomes may wander freely within the cytoplasm or attach to the endoplasmic reticulum, sometimes abbreviated as ER.
There are 2 types of ER: rough ER that has ribosomes attached to it and smooth ER which doesn't have ribosomes attached to it.

The endoplasmic reticulum is a membrane-enclosed passageway that transports materials such as ribosome-produced proteins.

Golgi Apparatus

Proteins and other materials emerge from the endoplasmic reticulum in small vesicles where the Golgi apparatus, sometimes called the Golgi body receives them. As proteins move through the Golgi body they're customized into forms that the cell can use. The Golgi body does this by folding the proteins into usable shapes or adding other materials on to them such as lipids or carbohydrates.

Vacuoles

Vacuoles are sac-like structures that store different materials. But in plant cell, the central vacuole stores water while animal cell has an organelle called a lysosome.

Lysosomes

Lysosomes are the garbage collectors that take in damaged or worn out cell parts. They contain enzymes that degrade this cellular debris.

Mitochondria

The mitochondria is an organelle that is the powerhouse for both animal and plant cells. During a process called cellular respiration the mitochondria make ATP molecules that provide the energy for all the cells activities. More mitochondria are found in cells that require more energy.

Cytoskeleton

The cell maintains its shape through a cytoskeleton. The cytoskeleton is made up of thread-like protein microfilaments and microtubules, which are thin hollow tubes.

Chloroplast

Some organisms such as plants that are photoautotrophic meaning they capture sunlight for energy have cells with an organelle called a chloroplast. Photosynthesis takes place in the chloroplast. It is green because it contains the green pigment chlorophyll.

Cell wall

Plant cells also have a cell wall outside of their cell membranes that shape, support, and protect the plant cell. A cell wall is never found in animal cells.

Cilia and Flagella

There are many other unique structures that only some cells have. Like in humans, for example, the respiratory tract is lined with cells that have cilia. These are tiny hair-like projections that move in waves. When you cough, this feature traps inhaled particles in the air and expels them. Flagella are another distinguishing feature of some cells. Flagella are found in some bacteria.

A flagellum is a small tail that can assist a cell in moving or propelling itself. The only human cell that has flagellum is a sperm cell.

Summary

eukaryotic cells are plant and animal cells with a nucleus and membrane-enclosed organelles While prokaryotic cells are unicellular organisms without these things. A cell membrane, cytoplasm, and genetic material are components of every cell. And even though only plant cells have chloroplasts both plant and animal cells have mitochondria