Plant and Animal cells

All living organisms are made up microscopic cells. Life begins with a cell and they are the building blocks of life. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells are either unicellular or multicellular. Cells function differently in unicellular and multicellular organisms. A unicellular organism depends upon just one cell for all of its functions while a multicellular organism has cells specialized to perform different functions that collectively support the organism. Summary:

• Unicellular = consists of one cell (amoeba).

Picture of a unicellular organism; examples are fungi ad bacteria Unicellular organisms include bacteria, protists, and yeast. For example, a paramecium is a slipper-shaped, unicellular organism found in pond water. It takes in food from the water and digests it in organelles known as food vacuoles. Nutrients from the food travel through the cytoplasm to the surrounding organelles, helping to keep the cell, and thus the organism, functioning.

• Multicellular = consists of millions – billions of cells (humans)

Multicellular organisms are composed of more than one cell, with groups of cells differentiating to take on specialized functions. In humans, cells differentiate early in development to become nerve cells, skin cells, muscle cells, blood cells, and other types of cells. One can easily observe the differences in these cells under a microscope. Their structure is related to their function, meaning each type of cell takes on a particular form in order to best serve its purpose. Nerve cells have appendages called dendrites and axons that connect with other nerve cells to move muscles, send signals to glands, or register sensory stimuli.  Outer skin cells form flattened stacks that protect the body from the environment. Muscle cells are slender fibers that bundle together for muscle contraction.

 

The cells of multicellular organisms may also look different according to the organelles needed inside of the cell. For example, muscle cells have more mitochondria than most other cells so that they can readily produce energy for movement; cells of the pancreas need to produce many proteins and have more ribosomes and rough endoplasmic reticula to meet this demand. Although all cells have organelles in common, the number and types of organelles present reveal how the cell functions.

All cells have a cell membrane. Inside the cell is a jelly-like fluid called the cytoplasm. Organelles are suspended in the cytoplasm and each organelle has a special function in the cell.

 

Tissue

A tissue is a group of cells that have the same structure and function. Animals are composed of tissue, such as nerve tissue and muscle tissue. Animals also contain blood, which is the only liquid tissue in animals. Plants contain different kinds of tissue, such as parenchyma and cork.

Organs

An organ is a group of tissues that have the same structure and function. Animals have organs, e.g. a heart, a brain, a stomach and a liver. Plants have organs, e.g. roots, stems, leaves and fruit.

Organizational levels of multicellular organisms

The relationship between cells, tissue and organs shows how a multicellular organism is organized. The first level of organization is the cell and the highest level of organization is the organ.

 

Plant and animal cell structures

We all understand by now that all living things have cells. Each individual organism and species have cells that are tailored for them and function in a way which helps the organism live.

Animal and plant cells both contain membrane-bound organelles such as nuclei and mitochondria. Plants and animals have different needs, so their cells do not look the same or contain the same organelles. Chloroplasts, for instance, are found in plant cells and are necessary to produce photosynthesis, but not in animal cells.

Typical Plant Cell:	A typical Animal Cell:

Let us distinguish the key differences of both plant and animal cells below:

• Although animals and plants both have mitochondria, only plants have chloroplasts. This means that, unlike animals, sunlight is the only source of sugar for plants; they can’t get it from food. Chloroplasts play an important role in this process (photosynthesis). A cell’s mitochondria breaks down sugar into energy by releasing it from the mitochondria. But on the other hand, an animal does not need chloroplasts, since sugar comes from food; only mitochondria are needed.
• Animal cells differ from one another, according to their own specialized function, for example, cells in liver tissue are different from cells in lung tissue.
• Plant cells differ from one another according to their function in the leaf, stem, root or flower.
• Cells also differ in size: from 2–15 micrometers in diameter (micrometer / micron, is one thousand times smaller than a mm: symbol = μ
• Both plant and animal cells contain vacuoles. The vacuole of a plant cell is used for storage and to keep the cell’s shape. Animal cells, however, contain more vacuoles, which are smaller.
• There is a cell wall and a membrane in plant cells. Cells of plants have an unusual rectangular shape as a result. However, there is no cell wall in animal cells, only a membrane.

 

Cells have three main parts or components:

• cell membrane (animal’s cells) / cell wall (plant cells)
• cytoplasm

 

Cell membrane (animal cells)

It is also called the plasmalemma or plasma membrane and is made up of made up of protein and fats. It is very thin, with tiny pores that allow certain substances to go into or out of the cell = semi-permeable.

 

Cell wall (plant cells)

Only plant cells have a cell wall = one of the main differences between plant and animal cells. The cell wall is situated outside the cell membrane, and the cell wall is not living tissue. It is made up of cellulose. Each plant cell has a primary cell wall, but as the cell ages, each plant cell forms secondary and tertiary cell walls:

• older cells have thicker walls than younger cells
• with woody plants, the outer two cell wall layers contain lignin, which makes
• the cell wall rigid and solid.

When secondary and tertiary cell walls form, no extra cellulose is deposited in certain places (known as pits). The pits allow cytoplasmatic threads (plasmodesmata) to go through from one plant cell to the next. The cytoplasmatic threads (plasmodesmata) allow water, glucose and amino acids to pass from one cell to the other.

Two plant cells are separated by another type of wall called the middle lamella; which is made up of pectose.

 

Cytoplasm

Cytoplasm is the jelly-like fluid content in the cell. The cytoplasm contains organelles with which each has its own function.

 

The nucleus

The nucleus is the ‘control centre’ of a cell. It is situated in the centre of the cell. It is also surrounded by a double membrane and nucleoplasma which is a fluid. The nucleus contains nucleoli. Each nucleolus contains RNA molecules that help with the production of proteins.

The nucleoplasma contains the chromatin network, which contains the DNA of the cell. DNA contains the hereditary material of the cell and determines what the cell looks like. The chromatin network plays a very important role during cell division

 

Cell organelles and their main functions

The cytoplasm of animal and plant cells has various organelles suspended in them:

• Endoplasmic reticulum (ER)
• Ribosomes
• Mitochondrion
• Golgi apparatus
• Lysosomes
• Plastids
• Vacuoles

 

Endoplasmic reticulum (ER)

Endoplasmic reticulum (ER) = a network of fine membranes that look like tubes. These tubes connect the cell membrane with the outer membrane of the nucleus.

• The ER is a transport system inside a cell.
• Different substances move through the ER inside of the cell.
• Sometimes there are small particles on the surface of the ER and they are called ribosomes.
• ER with ribosomes is called ribosomal ER or ‘rough ER’.
• Sometimes there are no ribosomes on the ER.
• The ER is then called ‘smooth ER’.

 

Ribosomes

Ribosomes are found on the surface of the ER. Some ribosomes can occur in small groups in the cytoplasm and such ribosomes are called polyribosomes (‘poly’ = many). They consist of RNA and contain enzymes. The enzymes are used to make proteins out of amino acids.

 

Mitochondrion

The mitochondrion is the ‘powerhouse’ of a cell. The process of respiration takes place inside the mitochondrion and during this process, molecules that contain energy are broken down and the energy is released. It’s important to remember that within the cell itself, the cell can use the energy to perform different functions. Cells that need more energy (e.g., cells is muscle tissue) have much more mitochondria than cells that do not need much energy.

Mitochondria have an oval or sausage shape and their walls consist of two membranes: the inner membrane and the outer membrane. The inner membrane has folds which called cristae. Respiration takes place on the surface of the cristae and the space between the two membranes is filled with liquid and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area for chemical reactions to occur on.

 

Golgi apparatus

Golgi apparatus is a collection of membranes stacked on top of one another (like pancakes). The golgi apparatus is normally situated close to the nucleus and works closely with the endoplasmic reticulum. The Golgi apparatus modifies proteins and brings them to the cell surface where they can be secreted. These secretions include hormones, enzymes, antibodies and other molecules. Cells that have a secretory function, for example gland cells, contain more of these organelles than other cells.

 

Lysosomes

Lysosomes are very similar to mitochondria. These are sac-like structures that have two membranes. Lysosomes are more often found in animal cells than plant cells. Liver cells (In animals) contain many lysosomes and they contain various enzymes that help with the digestion of large molecules, such as protein. These enzymes are responsible for the destruction of old cells and this process is known as autolysis.

 

Plastids

Plastids only appear in plant cells and they vary in size; in which they can be round, oval or disc-shaped.

There are three types of plastids:

• Chloroplasts: in the cells of all the green parts of a plant → contain chlorophyll, which gives plants their green colour. Chloroplasts are oval in shape and are surrounded by a single membrane. They also have an inner membrane. Photosynthesis takes place in the chloroplasts.
• Chromoplasts: Chromoplasts are responsible for the red, orange and yellow colour of many flowers, fruits and autumn leaves. Often called the ‘colour plastids. The colour is produced by a number of pigments. The most important pigments = carotenoids and xantophylls. Chromoplasts are important because: bright colours of flowers attract insects for pollination bright colours of fruits attract insects and animals that help in the distribution of seeds and another fact to note is that animals produce vitamin A from the carotenoids that they eat.
• Leucoplasts: plastids that contain no colour or chlorophyll. They only appear in cells that are not exposed to sunlight (e.g. the cells in the roots and seeds of plants). If leucoplasts are exposed to sunlight, they change into chloroplasts and start to produce chlorophyll (e.g. potatoes that start to turn green if they are exposed to sunlight). The main functions of leucoplasts = store nutrients (such as starch) and to manufacture oils and some proteins

 

Vacuoles

Vacuoles are hollow spaces in the cytoplasm filled with a watery fluid called cell sap. They occur in plant and animal cells, but are more well-developed in plant cells. Older cells have larger vacuoles than younger cells. Eventually, the vacuoles join to form one large, central vacuole. The tonoplast, a cytoplasmic membrane, surrounds the vacuoles. The cell sap consists of water, in which substances like sugars, salts, pigments and gases are dissolved.

 

The differences between plant and animal cells