Plant Cells

All living beings are composed of cells, but not all cells are alike. This article discusses the differences between plant and animal cells and the composition of plant cells.


HOW DO PLANT CELLS DIFFER FROM ANIMAL CELLS?

Cell Walls
Unlike animal cells, the cell walls of plants are composed of celllose, hemicellulose, pectin and in many cases lignin, which allows plants to more easily absorb and retain water. The cellulose is strong enough to handle a high degree of water pressure upon the cell wall. Animal cell walls are made up of a permeable plasma membrane.

Photosynthesis
Another big difference between animal and plant cells is that plants have chloroplasts which allow them to use sunlight to photosynthesize their own food. Animal cells don't have chloroplasts and must eat food, which their cells can then use to make energy and reproduce.

Vacuoles
Plant cells have one large vacuole, comprising most of the cell, which serves to hold and secrete both waste and nutrients. Animal cells have many smaller vacuoles within each cell.

Collagen vs. Pectin
Plant cells are bound together by molecules known as pectin. Animal cells are bound together by a protein known as colagen.


PLANT CELLS - BASIC STRUCTURE
In addition to their nucleus, plant cells also contain additional tiny cellular structures called organelles. These organelles carry out the various functions need for the cell to remain healthy.

The following is a glossary of plant cell anatomy terms:

Amyloplast - an organelle found in starchy plants, like tubers and fruits, that stores starch.

ATP - ATP is short for adenosine triphosphate; ATP is a high-energy molecule used for energy storage by organisms. In plant cells, ATP is produced in the cristae of mitochondria and chloroplasts.

Cell Membrane - a permeable plasma membrane which allows the cell to absorb nutrients and excrete waste.

Cell Wall - a thick, rigid membrane of celluslose fiber and other materials that surrounds a plant cell. The cell wall gives the plant cell most of its support and structure.

Centrosome - (also called the "microtubule organizing center") a small body located near the nucleus that has a dense center and radiating tubules. The centrosome is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. Unlike the centrosomes in animal cells, plant cell centrosomes do not have centrioles.

Chlorophyll - chlorophyll is a molecule that can use the light energy from sunlight to turn water and carbon dioxide gas into sugar and oxygen in a process called photosynthesis. Chlorophyll is magnesium based and is usually green.

Chloroplast - an elongated or disc-shaped organelle that contains chlorophyll. Photosynthesis (in which energy from sunlight is converted into chemical energy - or food) takes place in the chloroplasts.

Christae - (singular crista) the multiple-folded inner membrane of a cell's mitochondrion that are finger-like projections. The walls of the cristae are the site of the cell's energy production (it is where ATP is generated).

Cytoplasm - the gel-like substance that fills the cell. It is here that the nutrients are used.

Endoplasmic Reticulum - a large network of membranes which make up more than half of the cell membrane. There are two types of ER, "smooth" ER and "rough" ER. Smooth ER lacks ribosomes on the cytoplasmic surface, while rough ER has ribosomes studding the surface. Rough ER synthesizes and secretes serum proteins (like albumin) in the liver and hormones and other substances in the glands. Smooth ER is involved in the systhesis of phospholipids, is where the breakdown of toxins and carcinogens in the liver, the conversion of cholesterol into steroids, and the release of calcium ions inthe muscles. The smooth ER also transports the products of the rough ER to other parts of the cell, most notably the Golgi Body.

Golgi Complex - consists of flattened membranous sacs that are responsible for manufacturing, storing and shipping certain cellular products. It is here that the products of the endoplasmic reticulum are modified and sorted and then sent to their destination.

Granum - (plural grana) A stack of thylakoid disks within the chloroplast is called a granum.

Mitochondria - spherical to rod-shaped organelles with a double membrane that convert energy stored in glucose into ATP (adenosine triphosphate). The inner membrane is infolded many times, forming a series of projections called cristae.

Nucleus - a membrane-bound structure that is the "brain" of the cell which contains most of the genes that control the cell. The nucleus is enclosed by the nuclear envelope which keeps its contents separate from the cytoplasm. Inside the nucleus is a substance called chromatin which organizes DNA and proteins. When the cell begins reproduction, the chromatin thickens and becomes the separate structures known as chromosomes.

Nucleolus - a structure within the nucleus that helps in the synthesis of ribosomes

Nuclear membrane - the membrane that surrounds the nucleus.

Photosynthesis - a process in which plants convert sunlight, water, and carbon dioxide into food energy (sugars and starches), oxygen and water. Chlorophyll or closely-related pigments (substances that color the plant) are essential to the photosynthetic process.

Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly

Stroma - part of the chloroplasts in plant cells, located within the inner membrane of chloroplasts, between the grana.

Thylakoid disk - thylakoid disks are disk-shaped membrane structures in chloroplasts that contain chlorophyll. Chloroplasts are made up of stacks of thylakoid disks; a stack of thylakoid disks is called a granum. Photosynthesis takes place on thylakoid disks.

Vacuole - fluid-filled, membrane-surrounded cavities inside a cell. The vacuole fills with food being digested and waste material that is on its way out of the cell. Most plant cells have a single vacuole that takes up much of the cell. It helps maintain the shape of the cell.