Plant and Animal Cells
Biology is built on three simple but very important ideas. These three ideas form the cell theory. The cell theory states that
1. All living things are made up of one or more cells and their products.
2. The cell is the simplest unit that can carry out all life processes.
3. All cells come from other cells; they do not come from
non-living matter.
The simplest organisms are archaea and bacteria. These simple, single-celled life forms are called prokaryotes. The cells do not have a nucleus. More complex cells can exist as single-celled organisms or multicellular organisms. The cells of these organisms, known as eukaryotes, have a more complex internal organization, including a nucleus. The cells of eukaryotes are much larger than the cells of prokaryotes.
Cell Structure
Your body is made up of many specialized organs that carry out all the
processes needed to live.
Biology is built on three simple but very important ideas. These three ideas form the cell theory. The cell theory states that
1. All living things are made up of one or more cells and their products.
2. The cell is the simplest unit that can carry out all life processes.
3. All cells come from other cells; they do not come from
non-living matter.
The simplest organisms are archaea and bacteria. These simple, single-celled life forms are called prokaryotes. The cells do not have a nucleus. More complex cells can exist as single-celled organisms or multicellular organisms. The cells of these organisms, known as eukaryotes, have a more complex internal organization, including a nucleus. The cells of eukaryotes are much larger than the cells of prokaryotes.
Cell Structure
Your body is made up of many specialized organs that carry out all the
processes needed to live.
Structures Common to Plants and Animal Cells
All cells have to perform the same basic activities to stay alive: use energy, store materials, take materials from the environment, get rid of wastes, move substances to where they are needed, and reproduce. Each organelle has a
specific function within the cell. Just as workers in a factory or a hospital coordinate their efforts to achieve a purpose, the various organelles of a cell
work together to meet the needs of the cell—and the whole organism. The image, shows the organelles in a typical plant cell and a typical animal cell.
CYTOPLASM
All the organelles inside the cell are suspended in the cytoplasm. The cytoplasm is mostly water, but it also contains many other substances that
the cell stores until they are needed. Many chemical reactions take place within the cytoplasm, which can change from jelly-like to liquid, allowing organelles to be moved around.
All cells have to perform the same basic activities to stay alive: use energy, store materials, take materials from the environment, get rid of wastes, move substances to where they are needed, and reproduce. Each organelle has a
specific function within the cell. Just as workers in a factory or a hospital coordinate their efforts to achieve a purpose, the various organelles of a cell
work together to meet the needs of the cell—and the whole organism. The image, shows the organelles in a typical plant cell and a typical animal cell.
CYTOPLASM
All the organelles inside the cell are suspended in the cytoplasm. The cytoplasm is mostly water, but it also contains many other substances that
the cell stores until they are needed. Many chemical reactions take place within the cytoplasm, which can change from jelly-like to liquid, allowing organelles to be moved around.
CELL MEMBRANE
The cell is surrounded by a flexible double-layered cell membrane. The function of the cell membrane is both to support the cell and to allow some substances to enter while keeping others out. For example, water and oxygen molecules can easily pass through the cell membrane, but larger molecules, such as proteins, cannot. Because of this ability, the cell membrane is called a “semi-permeable membrane.”
The cell is surrounded by a flexible double-layered cell membrane. The function of the cell membrane is both to support the cell and to allow some substances to enter while keeping others out. For example, water and oxygen molecules can easily pass through the cell membrane, but larger molecules, such as proteins, cannot. Because of this ability, the cell membrane is called a “semi-permeable membrane.”
NUCLEUS
The nucleus is a roughly spherical structure within the cell. The nucleus contains genetic information that controls all cell activities. This genetic information is stored on chromosomes. Chromosomes contain DNA , the substance that carries the coded instructions for all cell activity. When a cell divides, the DNA is copied so that each new cell has a complete set of DNA.
The nucleus is a roughly spherical structure within the cell. The nucleus contains genetic information that controls all cell activities. This genetic information is stored on chromosomes. Chromosomes contain DNA , the substance that carries the coded instructions for all cell activity. When a cell divides, the DNA is copied so that each new cell has a complete set of DNA.
MITOCHONDRIA
Cells contain many mitochondria. Mitochondria are sometimes called the “power plants” of the cell because they
make energy available to the cell. Active cells, such as muscle cells, have more mitochondria than less active cells, such as fat-storage cells. Cells store energy as a form of glucose (a sugar). The mitochondria contain enzymes that help to convert the stored energy into an easily usable form. This process is called cellular respiration and requires oxygen. The waste products of this reaction are carbon dioxide and water. Usable energy Cells in which cellular respiration has to happen very fast, such as muscle cells and cells in the liver, have many mitochondria. In contrast, cells that are fairly inactive—that do not have to respire quickly—tend to have very few mitochondria. Fat cells may have only one or two mitochondria.
Cells contain many mitochondria. Mitochondria are sometimes called the “power plants” of the cell because they
make energy available to the cell. Active cells, such as muscle cells, have more mitochondria than less active cells, such as fat-storage cells. Cells store energy as a form of glucose (a sugar). The mitochondria contain enzymes that help to convert the stored energy into an easily usable form. This process is called cellular respiration and requires oxygen. The waste products of this reaction are carbon dioxide and water. Usable energy Cells in which cellular respiration has to happen very fast, such as muscle cells and cells in the liver, have many mitochondria. In contrast, cells that are fairly inactive—that do not have to respire quickly—tend to have very few mitochondria. Fat cells may have only one or two mitochondria.
ENDOPLASMIC RETICULUM
The endoplasmic reticulum is a three-dimensional network of branching tubes and pockets. It extends throughout the cytoplasm and is continuous from the nuclear membrane to the cell membrane.These fluid-filled tubes transport materials, such as proteins, through the cell. Endoplasmic reticulum is important in many types of cells. In the brain it assists with the production and release of hormones. In the muscles the endoplasmic reticulum is involved with muscle contraction.
The endoplasmic reticulum is a three-dimensional network of branching tubes and pockets. It extends throughout the cytoplasm and is continuous from the nuclear membrane to the cell membrane.These fluid-filled tubes transport materials, such as proteins, through the cell. Endoplasmic reticulum is important in many types of cells. In the brain it assists with the production and release of hormones. In the muscles the endoplasmic reticulum is involved with muscle contraction.
GOLGI BODIES
Golgi bodies collect and process materials to be removed from the cell. They also make and secrete mucus. Cells that secrete a lot of mucus, such as cells lining the intestine, have many Golgi bodies.
Golgi bodies collect and process materials to be removed from the cell. They also make and secrete mucus. Cells that secrete a lot of mucus, such as cells lining the intestine, have many Golgi bodies.
VACUOLES
A vacuole is a single layer of membrane enclosing fluid in a sac. The functions of vacuoles vary greatly, according to the type of cell. These functions include containing some substances, removing unwanted substances from the cell, and maintaining internal fluid pressure within the cell. Mature plant cells usually have one central vacuole that is visible under a microscope. Some animal cells can change their shape to wrap around and surround smaller objects to bring them inside the cell. Amoeba do this to obtain food. Some white blood cells engulf bacteria to kill them. During the engulfing process, a portion of the cell membrane turns inside out and forms a vacuole inside the cell until the engulfed object is digested. Then any waste material is ejected from the cell as the vacuole again joins up with the cell membrane.
A vacuole is a single layer of membrane enclosing fluid in a sac. The functions of vacuoles vary greatly, according to the type of cell. These functions include containing some substances, removing unwanted substances from the cell, and maintaining internal fluid pressure within the cell. Mature plant cells usually have one central vacuole that is visible under a microscope. Some animal cells can change their shape to wrap around and surround smaller objects to bring them inside the cell. Amoeba do this to obtain food. Some white blood cells engulf bacteria to kill them. During the engulfing process, a portion of the cell membrane turns inside out and forms a vacuole inside the cell until the engulfed object is digested. Then any waste material is ejected from the cell as the vacuole again joins up with the cell membrane.
Organelles in Plants Cells Only
Plant cells and animal cells have many structures in common, but there are also some differences. Plant cells have some organelles that animal cells do not
have.
Plant cells and animal cells have many structures in common, but there are also some differences. Plant cells have some organelles that animal cells do not
have.
CELL WALL
The cell wall is found just outside the cell membrane of a plant cell. It is a rigid but porous structure made of cellulose. This cell wall provides support for the cell and protection from physical injury. This tough material may hold together long after the plant has died.
The cell wall is found just outside the cell membrane of a plant cell. It is a rigid but porous structure made of cellulose. This cell wall provides support for the cell and protection from physical injury. This tough material may hold together long after the plant has died.
VACUOLE
Plant cells usually have one large vacuole, which takes up most of the space inside the cell. When these are full of water, turgor pressure keeps the cells
plump, which keeps the plant’s stems and leaves firm. If the water level drops, however, the vacuoles lose turgor pressure and the cells become soft . The plant stems and leaves become limp and droopy until the water is replaced.
Plant cells usually have one large vacuole, which takes up most of the space inside the cell. When these are full of water, turgor pressure keeps the cells
plump, which keeps the plant’s stems and leaves firm. If the water level drops, however, the vacuoles lose turgor pressure and the cells become soft . The plant stems and leaves become limp and droopy until the water is replaced.
CHLOROPLASTS
Many plant cells that are exposed to light, such as the cells of leaves, have structures called chloroplasts Chloroplasts contain chlorophyll and give leaves their green color. More importantly, chloroplasts absorb light energy. This light energy is used in photosynthesis—the process of converting carbon dioxide and water into glucose and oxygen. Photosynthesis allows plants to obtain their energy from the Sun so that they can make their own food. Plant cells rely on mitochondria to metabolize glucose, just as animal cells do.
Many plant cells that are exposed to light, such as the cells of leaves, have structures called chloroplasts Chloroplasts contain chlorophyll and give leaves their green color. More importantly, chloroplasts absorb light energy. This light energy is used in photosynthesis—the process of converting carbon dioxide and water into glucose and oxygen. Photosynthesis allows plants to obtain their energy from the Sun so that they can make their own food. Plant cells rely on mitochondria to metabolize glucose, just as animal cells do.