Biology : Plant & Animal Cells III (Parts & Functions)

1. Cell MembraneThe cell membrane is also known as the plasma membrane. It is the outermost covering of the animal cell. It protects the cell and regulates the entry and exit of substances, namely ions and solutes.

2. Cell WallThe cell wall is the outermost covering of the plant cell made up of cellulose, and surrounds the cell membrane. It protects the cell, provides mechanical support and is responsible for maintaining pressure inside the cell.

3. CentrosomeThe centrosome of the animal cell contains one or two centrioles, and is surrounded by microtubules or the centrosphere. It initiates and regulates cell division.

4. ChloroplastThe chloroplast of the plant cell is a green-colored plastid. Chlorophyll contained in the chloroplast captures energy from sunlight and helps in the manufacture of food by the process of photosynthesis.

5. ChromoplastThe chromoplast of the plant cell is a plastid that is colored differently in different cells. It contains pigments such as xanthophyll (yellow in color) and carotene (orangish-red in color). It imparts color to flowers and fruits of plants.

6. CytoplasmThe cytoplasm is composed of a mixture of water and soluble organic & inorganic compounds, and contains most of the cell organelles. It is the house of all metabolic functions and activities of the animal cell. 

7. Endoplasmic ReticulumThe endoplasmic reticulum consists of tubular structures (convoluted tubules) lying near the nucleus. It provides support to the plant cell and the animal cell. It is of two types, namely the smooth endoplasmic reticulum (does not have ribosomes attached to it) and the rough endoplasmic reticulum (has ribosomes attached to it).

8. Golgi ApparatusThe golgi apparatus of the animal cell consists of flat vesicular structures placed one on top of

the other. It synthesizes and secretes certain substances, namely hormones and enzymes.

9. LeucoplastThe leucoplast of the plant cell is a colorless plastid. It helps in the storage of starch.

10. LysosomeThe lysosome of the animal cell is a membranous sac budded off from the golgi apparatus, and contains several types of enzymes. It performs intracellular digestion and destroys foreign substances.

11. MitochondrionThe mitochondrion of the cell has two layers of membrane, of which the inner one is folded to

form cristae. It is the site of ATP (Adenosine triphosphate) synthesis.

12. Nuclear MembraneThe nuclear membrane is the covering of the nucleus of the cell, and has numerous pores. It allows substances to enter and leave.

13. NucleolusThe nucleolus is contained in the nucleus of the cell, and is round in shape. It synthesizes proteins by producing and storing RNA (Ribonucleic acid).

14. NucleoplasmThe nucleoplasm is a dense fluid containing chromatin fibres, which are made up of DNA (Deoxyribonucleic acid). After cell division takes place, these chromatin fibres undergo certain structural changes, and are called chromosomes. These chromosomes carry the hereditary information of the genes.

15. NucleusThe nucleus is the most important part of the cell, and contains large amounts of DNA (Deoxyribonucleic acid). It controls and coordinates all the activities and functions of the cell.

16. RibosomeThe ribosome is chiefly composed of RNA (Ribonucleic acid). It synthesizes proteins.

17. VacuoleThe vacuole of the plant cell is a very large and abundant vesicle. It is filled with fluids, and helps in the storage of water and other substances.

Cell Parts and Their Functions

Nucleus - Controls the cell.Nucleolus - Makes ribosomes, maybe more than one in a cell, found in the nucleus. Chromosomes- Determines what traits a living thing will have, passes information from parent to offspring. Cell Membrane - Gives the cell shape, holds the cytoplasm, and controls what moves into and out of the cell. Cytoplasm - Jellylike material (cytosol and organelles), most of the cell's chemical reactions take place there, and made up of mostly water and some chemicals. Vacuoles - Liquid-filled, may store food, water, minerals, or wastes. In plants it takes up a lot of space. There maybe more than one. Mitochondria - Produce energy when food is broken down, often called the "powerhouse of the cell". Ribosomes - Where proteins are made, and often connected to the endoplasmic reticulum. A cell may have as many as 500,000. Endoplasmic Reticulum - The "transportation system" in the cell, connects the nuclear membrane with the cell membrane. Used in detoxification of the cell. "ER" Centrioles - Found only in animal cells, is used in cell reproduction to help the chromosomes arrange before cell division. Cell Wall - Found only in plant cells. Forms a thick outer covering outside the cell membrane, gives the plant support and shape. Chloroplasts - Found only in plant cells. Found in the cytoplasm of green plant cells, contain chlorophyll, traps the energy from light, and is

where photosynthesis takes place. Lysosomes - digests food particles with enzymes, pinched of pieces of golgi apparatus Golgi apparatus (bodies)- flat stacks, packages and secretes from cell.

Cell Parts and Their Functions Nucleus - Large Oval body near the centre of the cell. - The control centre 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 fibre 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 - power house of the cell. - centre 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.

Eucaryotic Cell Organelles

Nucleus: The nucleus is the most obvious organelle in any eukaryotic cell. It is enclosed in a double membrane and communicates with the surrounding cytosol via numerous nuclear pores. Within the nucleus is the DNA responsible for providing the cell with its unique characteristics. The DNA is similar in every cell of the body, but depending on the specific cell type, some genes may be turned on or off - that's why a liver cell is different from a muscle cell, and a muscle cell is different from a fat cell. When a cell is dividing, the nuclear chromatin (DNA and surrounding protein) condenses into chromosomes that are easily seen by microscopy.

Nucleolus: The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus and take positions on the rough endoplasmic reticulum where they are critical in protein synthesis.

Cytosol: The cytosol is the "soup" within which all the other cell organelles reside and where most of the cellular metabolism occurs. Though mostly water, the cytosol is full of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors.

Cytoplasm: This is a collective term for the cytosol plus the organelles suspended within the cytosol.

Centrosome: The centrosome, or MICROTUBULE ORGANIZING CENTER (MTOC), is an area in the cell where microtubules are produced. Plant and animal cell centrosomes play similar roles in cell division, and both include collections of microtubules, but the plant cell centrosome is simpler and does not have centrioles.

During animal cell division, the centrioles replicate (make new copies) and the centrosome divides. The result is two centrosomes, each with its own pair of centrioles. The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a "spindle" which is responsible for separating replicated chromosomes into the two daughter cells.

Centriole (animal cells only): Each centriole is a ring of nine groups of fused microtubules. There are three microtubules in each group. Microtubules (and centrioles) are part of the cytoskeleton. In the complete animal cell centrosome, the two centrioles are arranged such that one is perpendicular to the other.

Golgi: The Golgi apparatus is a membrane-bound structure with a single membrane. It is actually a stack of membrane-bound vesicles that are important in packaging macromolecules for transport elsewhere in the cell. The stack of larger vesicles is surrounded by numerous smaller

 

vesicles containing those packaged macromolecules. The enzymatic or hormonal contents of lysosomes, peroxisomes and secretory vesicles are packaged in membrane-bound vesicles at the periphery of the Golgi apparatus.

Lysosome: Lysosomes contain hydrolytic enzymes necessary for intracellular digestion. They are common in animal cells, but rare in plant cells. Hydrolytic enzymes of plant cells are more often found in the vacuole.

Peroxisome: Peroxisomes are membrane-bound packets of oxidative enzymes. In plant cells, peroxisomes play a variety of roles including converting fatty acids to sugar and assisting chloroplasts in photorespiration. In animal cells, peroxisomes protect the cell from its own production of toxic hydrogen peroxide. As an example, white blood cells produce hydrogen peroxide to kill bacteria. The oxidative enzymes in peroxisomes break down the hydrogen peroxide into water and oxygen.

Secretory Vesicle: Cell secretions - e.g. hormones, neurotransmitters - are packaged in secretory vesicles at the Golgi apparatus. The secretory vesicles are then transported to the cell surface for release.

Cell Membrane: Every cell is enclosed in a membrane, a double layer of phospholipids (lipid bilayer). The exposed heads of the bilayer are "hydrophilic" (water loving), meaning that they are compatible with water both within the cytosol and outside of the cell. However, the hidden tails of the phosopholipids are "hydrophobic" (water fearing), so the cell membrane acts as a protective barrier to the uncontrolled flow of water. The membrane is made more complex by the presence of numerous proteins that are crucial to cell activity. These proteins include receptors for odors, tastes and hormones, as well as pores responsible for the controlled entry and exit of ions like sodium (Na+) potassium (K+), calcium (Ca++) and chloride (Cl-).

Mitochondria: Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract - in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type. Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds (cristae) as seen in the cross-section, above. The cristae greatly increase the inner membrane's surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP - the primary energy source for the cell.

Vacuole: A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In animal cells, vacuoles are generally small. Vacuoles tend to be large in plant cells and play several roles: storing nutrients and waste products, helping increase cell size during growth, and even acting much like lysosomes of animal cells. The plant cell vacuole also regulates turgor pressure in the cell. Water collects in cell vacuoles, pressing outward against the cell wall and producing rigidity in the plant. Without sufficient water, turgor pressure drops and the plant wilts.

Cell Wall (plant cells only): Plant cells have a rigid, protective cell wall made up of polysaccharides. In higher plant cells, that polysaccharide is usually cellulose. The cell wall provides and maintains the shape of these cells and serves as a protective barrier. Fluid collects in the plant cell vacuole and pushes out against the cell wall. This turgor pressure is responsible for the crispness of fresh vegetables.

Chloroplast (plant cells only): Chloroplasts are specialized organelles found in all higher plant cells. These organelles contain the plant cell's chlorophyll responsible for the plant's green color. Chloroplasts have a double outer membrane. Within the stroma are other membrane structures - the thylakoids. Thylakoids appear in stacks called "grana" (singular = granum).

Smooth Endoplasmic Reticulum: Throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products, is a vast network of membrane-bound vesicles and tubules called the endoplasmic reticulum, or ER for short. The ER is a continuation of the outer nuclear membrane and its varied functions suggest the complexity of the eukaryotic cell.The smooth endoplasmic reticulum is so named because it appears smooth by electron microscopy. Smooth ER plays different functions depending on the specific cell type including lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell contraction.

Rough Endoplasmic Reticulum: Rough endoplasmic reticulum appears "pebbled" by electron microscopy due to the presence of numerous ribosomes on its surface. Proteins synthesized on these ribosomes collect in the endoplasmic reticulum for transport throughout the cell.

Ribosomes: Ribosomes are packets of RNA and protein that play a crucial role in both prokaryotic and eukaryotic cells. They are the site of protein synthesis. Each ribosome comprises two parts, a large subunit and a small subunit. Messenger RNA from the cell nucleus is moved systematically along the ribosome where transfer RNA adds individual amino acid molecules to the lengthening protein chain.

Cytoskeleton: As its name implies, the cytoskeleton helps to maintain cell shape. But the primary importance of the cytoskeleton is in cell motility. The internal movement of cell organelles, as well as cell locomotion and muscle fiber contraction could not take place without the cytoskeleton. The cytoskeleton is an organized network of three primary protein filaments:

- microtubules- actin filaments (microfilaments)- intermediate fibers

PLANT CELL

Plant cells like animal cells are eukaryotic cells i.e. they contain membrane bound nuclei and cell organelles. Plant cell differs from the animal cell in having three distinctive structures – cell wall, vacuoles and plastids. Plant cells lack centrioles and intermediate filaments, which are present in animal cells.

Parts of a Plant Cell Structure

Plant cells are classified into three viz. parenchyma cells, collenchyma cells and sclerenchyma cells based on the structure and function. Now let us see the different parts of a plant cell.

Cell Wall - Cell wall is the outermost rigid layer composed of cellulose, hemicellulose, pectin and sometimes lignin. The function of cell wall is protection, structural support and also it helps in filtering mechanism.

Cell Membrane - Cell membrane also called as plasma membrane is present inside the cell wall and surrounds the cytoplasm. It connects the intracellular components with the extracellular environment and helps in protection and transportation.

Plasmodesmata - Plasmodesmatas are small openings, which connect plant cells with each other enabling transport and communication between them.

Vacuole - Vacuoles are large membrane bound compartments, which stores compounds and provides storage, excretory and secretory functions. The membrane surrounding vacuole is called tonoplast.

Cytoplasm - Cytoplasm is filled up by cytosol, which is a gelatinous, semitransparent fluid.

Nucleus - Nucleus is a specialized organelle, which contains the plant’s hereditary material i.e. DNA (Deoxyribonucleic Acid). It also contains structures, which regulates the cell cycle, growth, protein synthesis and reproductive function.

Plastid - Plastids are organelles responsible for the photosynthetic activity and for the manufacture and storage of chemical compounds in plants. Chloroplast is an important form of plastid containing chlorophyll pigment, which helps in harvesting light energy and converting it to chemical energy.

Mitochondria - Mitochondria are oblong shaped organelles that are also known as "the powerhouse of

the cell". They are responsible for breaking down the complex carbohydrate and sugar molecules to simpler forms that the plants can use.

Endoplasmic Reticulum - Endoplasmic reticulum is an organelle responsible for the manufacturing and storage of chemical compounds like glycogen and steroids, translation and transportation of protein. It is also connected to the nuclear membrane so as to make a channel between the cytoplasm and the nucleus.

Golgi Apparatus - Golgi apparatus also known as golgi complex is an organelle responsible for the processing and packaging of macromolecules such as proteins and fats, which are synthesized by the cell and prepares them for transportation.

Ribosome - Ribosomes are organelles, which are made up of 60% RNA (Ribonucleic Acid) and 40% protein and play an important role in protein translation.

Microbodies - Microbodies are single membrane bound organelles, globular in shape and contains degradative enzymes. Most common microbodies are peroxisomes.

Microtubules - Microtubules are straight, hollow, tubular cylinders, which make up the cytoskeleton. They are responsible for structural support and transport of the cell.

Microfilaments - Microfilaments are thin filaments of the cytoskeleton and are responsible for structural support of the cell.

Plant Cell Diagram

The most vital plant cell structure and function is the preparation of food with the aid of plastids which what makes it a unique eukaryotic cell type.

Nucleus: The cell nucleus is supposed to be the most important plant cell organelle. It carries the genetic information present in this organelle which inherits the physical traits from one generation to another. It has a dark stained nucleolus mainly responsible for protein formation. Apart from this, the nucleus coordinates all the cell

functions and regulates the metabolism of plants. The passage of food and water and the influx of nutrients in and out of the cells are some of the characteristic functions of a plant cell.

Nuclear Membrane: As the name indicates, this membranous sheath surrounding the nucleus protects it from physical damage. You can go through the nuclear membrane function for better understanding.

Cytoplasm: As seen from this plant cell model, the cytoplasm of a cell is the ground substance or the matrix which is jelly like material in which all the cell organelles are embedded and suspended. The main cytoplasm function in a cell is to keep all the cell constituents intact.

Cell Membrane: Similar to a nuclear membrane, the main cell membrane function is to give the cell an appropriate shape and size. This thin membrane is made up of cellulosic fibers and proteins and its main function is transport of materials through cells.

Cell Wall: The cell wall is a distinguishing plant cell part which is not present in animals and mainly responsible for imparting rigidity to the cells. The cell wall material differs with plant species and gives a definite plant cell shape (elongated, oval, round, rectangular, squarish).

Plastids: Another peculiar organelle present in plant cells are the plastids. As mentioned before, plants prepare their own food with a unique process called photosynthesis with the aid of these plastids. The plastids consist of pigments which absorb light and make food. The most common plastid is chloroplast containing the green pigment chlorophyll.

Mitochondria: Mitochondria are among the largest cell organelles also known as the engine house or the energy house of the cells. These organelles provide the energy required for all the cellular activities by breaking down complex carbohydrates prepared during photosynthesis (glucose to energy).

Ribosomes: Ribosomes is the main site for protein synthesis since these are rich in ribonucleic acids. These organelles could be bound to the endoplasmic reticulum or free floating in the cytoplasm.

Endoplasmic Reticulum (ER): The plant cell model clearly suggests ER to be the second largest cell organelle after mitochondria since these form a series of interconnecting flattened tubular tunnels or sacs; rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The RER is mainly responsible for holding onto the proteins formed in the ribosomes, and transportation.

Golgi Apparatus: The proteins formed and bound by the ER need to be processed so as to perform normal functions. Golgi membranous sacs or dictyosomes chiefly associated with ER release protein chains after processing them.

Vacuoles: Plant cells are characterized by larger and lesser number of vacuoles and mainly responsible for maintaining the fullness of a cell. An alternative function of these is to store ions, sugars and secondary metabolites.

I hope this article on plant cell structure and function has given you the gist of the plant cell functions and parts. You will understand better with the help of the above labeled diagram.

Plant Cell and Animal Cell Similarities

cell Membrane: A cell membrane is found in both plant and animal cells. Also known as plasma membrane or plasmalemma, it is the outermost covering in an animal cell, while it lies next to the cell wall in a plant cell. The major functions of the cell membrane are giving shape to the cell, protection of the organelles and transportation of nutrients from inside the cell to the outside and vice versa. Know more on plasma membrane structure.

Nucleus: Nucleus, the control center of the cell, is a spherical shaped organelle, shared by plant and animal cells in common. It houses the chromosomes, which are the hereditary material of an organism. Also, protein synthesis begins in the nucleus, which is further continued and completed in the cytoplasm of the cell. Approximately 10 percent of the volume of the cell is concentrated in the nucleus. Know more on cell nucleus: structure and functions.

Cytoplasm: Cytoplasm is a semitransparent fluid between the nucleus and the plasma membrane. Found in plants and animals, the organelles are suspended in the cytoplasm of the cell. It is the medium for various biochemical reactions, which are important to promote cell growth and development. Know more on structure and functions of cytoplasm.

Mitochondria: Plant and animal cell similarities also include the presence of the mitochondria in the cytoplasm. Commonly referred to as powerhouse of the cell, the mitochondria is crucial to convert foods into usable forms of energy (adenosine triphosphate or ATP). This organelle also contains deoxyribonucleic acid (DNA), hence plays an important role in transmission of genetic characters from parents to the offspring. Know more on mitochondrial DNA.

Ribosomes: Ribosomes are another important cell organelle present in plants and animals. They are either scattered in the cytoplasm (free ribosomes) or found attached to the endoplasmic reticulum (bound ribosomes). Both types of ribosomes are crucial for synthesis of proteins according to the directions of the messenger ribonucleic acid (mRNA).

Endoplasmic Reticulum: Endoplasmic reticulum comprises of stacks of membranous tubules called cisternae. They are structures that connect the nucleus and cytoplasm. There are two types of endoplasmic reticulum - one without ribosomes (smooth endoplasmic reticulum or SER) and another with attached ribosomes (rough endoplasmic reticulum or RER).

Golgi Bodies: Golgi bodies are present in both plant cells and animal cells. They contain stacks of cisternae, hence they are also known as golgi complex or golgi apparatus. They play the role of modifying chemical substances and transporting them in and out of the cell. Know more on similarities between plant and animal cells.

Structure-wise, a plant cell contains more parts than an animal cell. And function-wise, they perform respiration and other common metabolic activities. With this brief information, I hope you have clearly understood the plant and animal cell similarities.

Plant Cell and Animal Cell Differences

For a lay man, the primary difference between plants and animals is that the former remains fixed, while the latter has the ability to move themselves from one place to another. But, there is more to this that differentiates a plant from an animal, in terms of their cell anatomical structure and parts. Listed below are some of the distinguishing features between a plant cell and an animal cell

Cell Shape and DivisionThe shape of a plant cell is more or less rectangular, while that of an animal cell is circular. And the mode of cell division or cytokinesis in a plant cell is different from the animal cell. Cytokinesis in a plant cell takes place by formation of a cell plate, whereas it occurs with formation of a cleavage furrow in an animal cell.

Cell WallCell wall is present in a plant cell, while it is absent in an animal cell. It is the outermost rigid, cellulose covering of the plant cell that provides protection and gives a definite shape. In an animal cell, the outer covering is plasma membrane, but not the plant cell. In brief, a plant cell has both a cell wall and plasma membrane, whereas an animal cell has only the plasma membrane.

ChloroplastA major difference between a plant cell and an animal cell is the presence of chloroplast in plants, while it is absent in case of animals. It is the chloroplast in plants, which is responsible for harvesting light from the sun and performing photosynthesis in the presence of water and carbon dioxide. Thus, by means of photosynthesis, sugar is produced by plants and is circulated in the food chain.

PlastidsThe organelle plastids are present in the cell of algae and plants, while they are absent in an animal cell. Plastids are responsible for production and storage of chemical compounds, including the plant pigments. Based on the type of plastids, the color of the cell varies. For example, chloroplasts are a type of plastids that are green in color.

VacuoleAnother significant plant and animal cell difference is the presence of a large sized vacuole in a plant cell, while it is not so in an animal cell. The vacuole in a plant cell occupies about 90 percent volume and performs a specific function. In an animal cell, vacuoles are small, insignificant and many in number. Read more on plant cell organelles.

Cilia and CentriolesCilia are hairlike, locomotive projections present on the external surface of a cell. These projections are absent in a plant cell, whereas an animal cell has cilia in its outer surface. Similarly, the organelle centrioles are present in an animal cell, while it is absent in a plant cell.

LysosomesLysosomes are organelles not evident in a plant cell, while they are found in an animal cell. These lysosomes are present in the cytoplasm of an animal cell and store enzymes for the breaking down of nutrient molecules.

Animal cell

The cell membrane is located around the outside of the cell. It is a protein lipid bilayer. The hydrophilic heads of the lipids point outwards while the hydrophobic tails occupy the space between the two lipid layers. Several types of proteins are imbedded in the membrane: channel, transport, recognition, receptor, and electron transfer. Channel proteins provide passageways through the membrane for small substances to diffuse through. Transport proteins are involved in the active transport of substances across the membrane. Recognition proteins recognize other cells. Receptor proteins are receptor sites for hormones and other chemicals. Electron transfer proteins are involved in the transfer of electrons in processes like photosynthesis and cellular respiration. Because the proteins constantly shift throughout the cell membrane, it is referred to as a fluid mosaic model. The functions of the cell membrane include: holding cellular material, regulating the movement of materials across the membrane, providing a surface for many chemical reactions, and identifying the cell to the body's immune system.

Cell junctions connect one cell to another. Gap junctions are found in animals and are very, very small channels that allow various ions and other small substances to pass from one cell to another. Tight junctions are seals around cells to prevent leakage. They are important for containing liquids like stomach acids. Desmosomes are spot welds that hold cells together.

The nucleus controls the cell's activities and contains all the genetic material (46 chromosomes in humans).

The nucleolus is involved in the synthesis of ribosomal RNA. It is a dark body inside the nucleus.

The nuclear membrane keeps DNA inside the nucleus but allows mRNA and proteins through. It is a double membrane with large pores.

Ribosomes assemble proteins from RNA codes. They are found free-floating in the cytoplasm throughout the cell or attached to the endoplasmic reticulum.

The smooth endoplasmic reticulum is a series of long canals running throughout the cell. It detoxifies the cell and converts foodstuffs.

The rough endoplasmic reticulum is a series of long canals running throughout the cell with ribosomes attached. It transports proteins to the golgi bodies for packaging.

Golgi bodies (also apparatus or complex) store and package cellular secretions for export out of the cell (usually through the use of vacuoles). Salivary, oil, and digestive glands have very active golgi bodies.

Lysosomes digest and remove worn out cell organelles. In essence, they are vacuoles filled with digestive enzymes.

Mitochondria produce most of the cell's energy. They are composed of two membranes (an outer and a folded inner membrane) and are common in muscle cells.

Centrioles anchor spindle fibers during cell division. They are composed of microtubules and are only found in animal cells.

The cell's cytoskeleton provides the cell with shape and support. It is involved in cell movement (cytoplasmic streaming, muscle contraction, ameboid movement, and cell division). The cytoskeleton is composed of actin filaments, intermediate filaments, and microtubules.

Vacuoles are "bubbles" of material in the cell. Usually vacuoles hold water. They can, however, hold solutions and solid material as well.

Some cells have microvilli to aid in movement or absorption\\

Plant cells have all of the same organelles as animal cells except:

Plant cells don't have centrioles.

Plant cells have another kind of cell junction called plasmodesmata.

Plants have leucoplasts that store starch, oil, or protein.

Plants have chloroplasts that are active in photosynthesis. Chloroplasts have a double membrane and contain chlorophyll.

Plants have cell walls made of cellulose in addition to cell membranes. (Note: bacteria have cell walls made of peptidoglycan and fungi have cell walls made of chitin)

Water vacuoles in plants are much larger and support much of the cell.

Bacterial Cell Structure

 

 

 

Internal Structure: Bacteria have a very simple internal structure, and no membrane-bound organelles.

nucleoidDNA in the bacterial cell is generally confined to this central region. Though it isn't bounded by a membrane, it is visibly distinct (by transmission microscopy) from the rest of the cell interior.

ribosomes

Ribosomes give the cytoplasm of bacteria a granular appearance in electron micrographs. Though smaller than the ribosomes in eukaryotic cells, these inclusions have a similar function in translating the genetic message in messenger RNA into the production of peptide sequences (proteins).

storage granules

(not shown) Nutrients and reserves may be stored in the cytoplasm in the form of glycogen, lipids, polyphosphate, or in some cases, sulfur or nitrogen.

endospore

(not shown) Some bacteria, like Clostridium botulinum, form spores that are highly resistant to drought, high temperature and other environmental hazards. Once the hazard is removed, the spore germinates to create a new population.

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Surface Structure: Beginning from the outermost structure and moving inward, bacteria have some or all of the following structures:

capsule

This layer of polysaccharide (sometimes proteins) protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells.

outer membrane

(not shown) This lipid bilayer is found in Gram negative bacteria and is the source of lipopolysaccharide (LPS) in these bacteria. LPS is toxic and turns on the immune system of , but not in Gram positive bacteria.

cell wall Composed of peptidoglycan (polysaccharides + protein), the cell wall maintains the overall shape of a bacterial cell. The three primary shapes in bacteria are coccus (spherical), bacillus (rod-

shaped) and spirillum (spiral). Mycoplasma are bacteria that have no cell wall and therefore have no definite shape.

periplasmic space

(not shown) This cellular compartment is found only in those bacteria that have both an outer membrane and plasma membrane (e.g. Gram negative bacteria). In the space are enzymes and other proteins that help digest and move nutrients into the cell.

plasma membrane

This is a lipid bilayer much like the cytoplasmic (plasma) membrane of other cells. There are numerous proteins moving within or upon this layer that are primarily responsible for transport of ions, nutrients and waste across the membrane.

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Appendages: Bacteria may have the following appendages:

pili

These hollow, hairlike structures made of protein allow bacteria to attach to other cells. A specialized pilus, the sex pilus, allows the transfer of plasmid DNA from one bacterial cell to another. Pili (sing., pilus) are also called fimbriae (sing., fimbria).

flagella

The purpose of flagella (sing., flagellum) is motility. Flagella are long appendages which rotate by means of a "motor" located just under the cytoplasmic membrane. Bacteria may have one, a few, or many flagella in different positions on the cell.