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3.1: How Cells Are Studied
In multicellular organisms, several cells of one particular kind interconnect with each other and perform shared functions to form tissues (for example, muscle tissue, connective tissue, and nervous tissue), several tissues combine to form an organ (for example, stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems functioning together form an organism (such as an elephant, for example).
3.2: Comparing Prokaryotic and Eukaryotic Cells
Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro- = before; -karyon- = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes (eu- = true).
3.3: Eukaryotic Cells
At this point, it should be clear that eukaryotic cells have a more complex structure than do prokaryotic cells. Organelles allow for various functions to occur in the cell at the same time. Before discussing the functions of organelles within a eukaryotic cell, let us first examine two important components of the cell: the plasma membrane and the cytoplasm.
3.4: The Cell Membrane
The plasma membrane is referred to as the fluid mosaic model and is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane. These function to identify other cells.
3.5: Passive Transport
The most direct forms of membrane transport are passive. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement. In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion. A physical space in which there is a different concentration of a single substance is said to have a concentration gradient.
3.6: Active Transport
Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient, that is, if the concentration of the substance inside the cell must be greater than its concentration in the extracellular fluid, the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight material, such as ions, through the membrane.
Cell Structure and Function Worksheet Answers Chapter 3
In the Work At Home Made Easy book, Cell Structure and Function Worksheet Answers, you will learn how to understand cells using the formulas in Microsoft Excel. You will also learn how to fill, calculate, and format cell with the help of formulas.
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In this chapter, you will be able to learn how to identify the cell structure and function of a particular range. You will also learn how to use the cell’s style as an identifier to make things easier for you.
One of the first steps is to use a format row in the right-hand side of the worksheet. There are two forms of this sheet: the row format worksheet and the column format worksheet. To use the row format worksheet, you have to click on Format > Rows.
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Next, locate the cell where you want to find the data. Then, press CTRL+A to select the cell and then go to Format > Cells. The other option is to press Ctrl+C.
After that, insert or delete the first cell. You can use the mouse to point at the area you want to modify. You can change the style of the cell as well.
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When you have inserted the cell, you can use the default style of the cell. For the second type of cell, you can use the style sheets.
The style sheets will let you adjust the formatting of the cells in accordance with your needs. Once you have added the style sheets, you can find that it will allow you to customize the formatting of all the cells. However, you must set the style sheets to the default style before you can edit the style of the cells.
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Finally, we will continue to learn about cell structure and function in a subsequent article. You will learn how to work with the ROWS formula to apply formatting on the cells.
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Cell Review Guide (Answers)
a. endoplasmic reticulum - transport within cell
b. mitochondria - produces energy, ATP (powerhouse)
c. ribosomes - makes proteins
d. nucleolus - makes ribosomes
e. microfilaments & microtubules - cytoskeleton, support
f. lysosomes - contains enzymes to break down materials
g. golgi apparatus - packaging and export of proteins in vesicles
h. centrioles - moves chromosomes during cell division
2. The basic unit of structure and function in the human body is the ____ cell _______
3. Describe each of these processes: phagocytosis - consuming large food particles , pinocytosis - consuming large liquid particles , exocytosis - pushing waste or vesicles out of the cell
4. What is the difference between active transport and passive transport? Give a specific example of each type.
active transport - requires energy ATP sodium-potassium pump, endocytosis, exocytosis
passive transport - does not require energy diffusion and osmosis
5. Describe the process of making and exporting a protein from a cell.
proteins are made by the ribosomes and then transported through the endoplasmic reticulum where they are packaged into vesicles by the golgi apparatus. Vesicles are exported out of the cell (exocytosis)
6. Describe the cell membrane and its properties. What is its function?
the cell membrane is selectively permeable, it consists of phospholipids and proteins arranged in a bilayer, it regulates what comes into and out of the cell
7. What is diffusion and facilitated diffusion? What is osmosis?
diffusion is the movement of molecules from areas of high concentration to low, molecules tend to spread out
faciliatated diffusion uses proteins in the membrane to help move molecules across
osmosis is the diffusion of water
8. List and describe the stages in the life cycle of a cell.
interphase - resting phase, cell makes a copy of DNA
prophase -chromatin condenses in chromosomes, spindle forms
metaphase - chromosomes line up along the equator
anaphase - chromatids separate
telophase - cell begins to pinch inward, nuclear membrane reforms, spindle disappears cytokinesis begins
9. What is the centriole and the spindle and what is their role in cellular reproduction? structures that move chromosomes so that each new daughter cell gets the correct number
10. What is the difference between chromosomes, chromatin, and chromatids?
chromosomes look like X's and appear during prophase, chromatin is DNA, a chromatid is a single copy (half of the X) that is visible during prophase and eventually separates during anaphase
11. What is DNA and what do the letters stand for? deoxyribonucleic acid
12. Explain the process of cellular respiration and why it is important for the cell. Cellular respiration uses oxygen and glucose to create ATP, ATP is necessary for many of the cell function, like the active transport. Respiration occurs in the mitochondria.
13. What is the difference between hypertonic, hypotonic, & isotonic? What will happen to cells placed in each type of solution?
isotonic - solution has an equal concentration as the cell, no net movement
hypertonic - solution has a greater number of solutes, this causes water to move out of the cell
hypotonic - solution has fewer solutes, this causes water to move into the cell
Remember the rule: SALT SUCKS
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PURPOSE OF THE STUDY
RQ1: How do students coenrolled in introductory chemistry and biology courses describe the meanings of the terms “structure,” “properties,” and “function”?
RQ2: How do students coenrolled in introductory chemistry and biology compare their experiences with regard to the presentation of structure, properties, and function (and the relationship between them) in these courses?
RQ3: How do students coenrolled in introductory chemistry and biology courses describe the relationship between structure, properties, and function?
These research questions are deeply interconnected, as students’ interpretation of the meaning of the component terms would likely affect their understanding of the relationships presented in their courses and vice versa. Together, this understanding of the terms in context and the presentation of the relationships between them would likely affect how and whether they develop a coherent understanding that spans the disciplines.
Cell Worksheets | Plant and Animal Cells
This collection of animal and plant cell worksheets strikes a balance between cognitive and psychomotor domains of learning and offers a conceptual grounding in cell biology. The worksheets recommended for students of grade 4 through grade 8 feature labeled animal and plant cell structure charts and cross-section charts, cell vocabulary with descriptions and functions and exercises like identify and label the parts of the animal and plant cells, color the cell organelles, match the part to its description, fill in the blanks, crosswords and more. Diffuse into a cell with our free worksheets!
Featured in this printable worksheet are the diagrams of the plant and animal cells with parts labeled vividly. This enhanced visual instructional tool assists in grasping and retaining the names of the cell parts like mitochondrion, vacuole, nucleus and more with ease.
How does a minute cell accomplish complex tasks? Learn about the various organelles and the function of each part of the cell with this cell terminology PDF for 7th grade and 8th grade students.. Included here are apt and precise definitions of cell, cell wall, cell membrane, Golgi apparatus and more.
What is the difference between a plant cell and an animal cell? The t-chart for students of grade 7 and grade 8 provides the answer to this question and lists the differences between a plant and an animal cell.
Learn the parts of a plant cell easily with this cross-section of a plant cell diagram. The clearly marked parts like chloroplast, endoplasmic reticulum and more help reinforce the cell terminology and spellings.
This follow-up activity pdf worksheet on labeling the parts of a plant cell assists in testing the knowledge of 5th grade and 6th grade students. The students are expected to identify the 10 parts marked and name them with words from the word bank.
Twelve major plant cell parts have been marked. Identify the organelles and the parts and label them in this printable worksheet. Test comprehension and reiterate the concept with this plant-cell-labeling worksheet for students of grade 8.
Review skills in identifying the parts and organelles of a plant cell with this printable worksheet. The students are expected to recognize the seven major plant cell parts like vacuole, nucleus, mitochondrion and more. Color them using the color key to complete the worksheet.
This vibrant worksheet contains the cross-section of an animal cell, vividly displaying the organelles. Examine the animal cell diagram and recognize parts like the centrioles, lysosomes, Golgi bodies, ribosomes and more indicated clearly.
Labels are important features of any scientific diagram. The students of grade 5 and grade 6 are expected to select the correct label from the word bank to name each of the ten indicated parts to complete the worksheet.
Recapitulate the names of the twelve major parts of an animal cell with this worksheet. Students examine the animal cell diagram, identify the marked significant parts and write their names.
Recognize the seven animal cell organelles featured in the word box, color them using the color key in this interesting activity PDF. This cell organelle worksheet provides a fun way to tell apart each cell organelle.
The cell parts or organelles are stated in one column and the other column has the nicknames or the expressions that best describe them. Correlate the two and understand the function of each part as well.
This fill in the blanks worksheet consists of 15 cell facts. Read each sentence carefully and supply the missing word(s). Hone your knowledge with facts related to cells and test comprehension of students with this worksheet.
Experience the language of science and review the cell terminology with this printable crossword worksheet for 4th grade and 5th grade students. Read each clue carefully, understand the function stated, identify the part or organelle responsible and write its name in the crossword grid provided.
NCERT Solutions Class 8 Science Chapter 8 are prepared by the subject experts at Vedantu to help students get a clear understanding of the topics covered in the chapter. Students can consult with the revision notes provided in this text. The solved exercises are going to help students prepare the chapter for their exams. With the help of the NCERT Solutions for Chapter 8 Class 8 Science "Cell structure and function" students can learn and understand the chapter thoroughly. Also, they can download these NCERT Solutions for free of cost from Vedantu.
The solutions for NCERT Class 8 Science Chapter 8 Cell structure and functions will be a useful resource for you in revising the chapter quickly to get clarity on the chapter before the examinations. Keep in mind to practice it daily. These NCERT solutions will help you develop your pace of writing answers to the questions and boost your confidence for the exam.
Students can also download NCERT Solution PDF for all subjects to prepare for their forthcoming exams. Maths Students who are looking for the better solutions ,they can download Class 8 Maths NCERT Solutions to help you to revise complete syllabus and score more marks in your examinations.
Lactate as a signal?
It appears that we still do not fully understand all of the roles for lactate in vivo. Whilst much of the data presented so far have been gleaned from isolated muscle, or cell culture, understanding how these observations transfer to the whole organism is perhaps the next important question to be addressed.
Suggestion of a role for lactate as a metabolic signal at the whole-organism level has been postulated by Brooks(2002a), who proposed that lactate may operate as a pseudo-hormone. Within this model, blood glucose and glycogen reserves in diverse tissues are regulated to provide lactate, which may then be used within the cells where it is made or transported through the interstitium and vasculature to adjacent or anatomically distributed cells for utilization. In this role, lactate becomes a quantitatively important oxidizable substrate and gluconeogenic precursor, as well as a means by which metabolism in diverse tissues may be coordinated. Lactate has the ability to regulate cellular redox state, via exchange and conversion into its more readily oxidized analogue, pyruvate, and effects on NAD + /NADH ratios. Lactate is released into the systemic circulation and taken up by distal tissues and organs, where it also affects the redox state in those cells.
Further evidence for lactate acting as something more than a metabolite or metabolic by-product comes from wound repair research, where lactate appears to induce a biochemical `perception' effect(Trabold et al., 2003). It had been suggested that the elevated acidosis associated with wound regeneration was a result of localised hypoxia. However, Trabold et al.(2003) provided evidence that lactate may act as a stimulus similar to hypoxia without any compromise to O2 levels. Green and Goldberg(1964) demonstrated that collagen synthesis rose ∼2-fold in lactate-incubated (15 mmol l –1 ) fibroblasts, whilst Constant et al.(2000) showed that increased lactate was capable of upregulating vascular endothelial growth factor (VEGF)in similar proportions. To examine this apparent relationship, Trabold et al.(2003) elevated extracellular lactate in the wounds of male Sprague-Dawley rats by implanting purified solid-state, hydrolysable polyglycolide. This substance raised localised lactate to a maintained 2–3 mmol l –1 . Elevating lactate resulted in elevations in VEGF and a 50% increase in collagen deposition over a 3-week period. These data suggest that lactate is capable of inducing responses characteristic of O2 lack, operating to instigate a pseudo-hypoxic (as far as concentration of lactate is concerned) environment. In combination with this action, the continued presence of molecular oxygen(as the tissue was not hypoxic) allows endothelial cells and fibroblasts to promote increased collagen deposition and neovascularization.
The possibility that lactate acts as a metabolic signal is important to take research further. Based on the hypotheses of Trabold et al.(2003) and Brooks(2002a), can a working model of lactate signalling be extended to systemic and localised exercise function?
Interacting processes suggested to be involved with increased lactate accumulation during exercise.
Interacting processes suggested to be involved with increased lactate accumulation during exercise.
Firstly, lactate could, potentially, influence local and central blood flow during exercise. Hypoxia is known to stimulate systemic vasodilation via a host of neural, hormonal and local factors(Skinner and Marshall, 1996). Fattor et al. (2005) have recently used the lactate clamp method to demonstrate an autoregulatory loop in sympathetic drive that is governed by lactate release. Circulatory norepinephrine was reduced during exercise at 65%V̇O2 peak when lactate was maintained at 4 mmol l –1 compared with controls(2.115±166 pg ml –1 to 930±174 pg ml –1 , respectively), with epinephrine concentrations displaying a similar trend (EX 262±37 pg ml –1 to LC113±23 pg ml –1 ). This lends evidence to the possibility of modulatory control of catecholamines by lactate. The infusion of lactate had no effects on other glucoregulatory hormones (i.e. insulin and glucagon) or cortisol. The authors suggest that the lactate anion was sensed by either the ventromedial hypothalamus (VMH) or elsewhere vianeuronal metabolism signalling abundant fuel supply however, this theory remains to be tested. Therefore, the release of lactate into the circulation at the onset of exercise could promote vasodilation, allowing oxygenated blood to reach active muscle, acting in an additive or modulatory manner to the demands of tissues during exercise.
1. ENDOPLASMIC RETICULUM (E.R.) - complex system of canals and channels
A. Rough ER - where ribosomes are located
Ribosomes make ___________________
B. Smooth ER - no ribosomes, where lipid synthesis takes place
2. GOLGI APPARATUS (BODIES) - flattened membranes, the droplets on the edges of the G.A. are vesicles
3. MITOCHONDRIA (-ion = sing.) - the "powerhouse" of the cell, harvests energy
Function = energy from food is converted to ___________
This process is called ________________
Cellular respiration requires glucose (food) and _______________
What are symptoms of mitochondrial disease? Does Mackenzie have these symptoms?
4. LYSOSOMES -. Contain _____________________ sometimes called the "suicide sac
What is the purpose of enzymes?
What organ of your body is most like the lysosome?
What causes Tay-Sachs disease? Does Mackenzie have these symptoms?
5. CENTROSOME (centrioles)) -Composed of 2 "cylinders" which lie perpendicular to each other Involved in
During cell division - centrioles form a ___________________________
6. CYTOSKELETON Made of microtubules and microfilaments that give the cell support and shape.
What two structures function in movement? Describe or sketch them
What is Primary Ciliary Dyskinesia?
How does this condition result in &ldquositus inversus?&rdquo
Why would PCD make it difficult to get pregnant or have a baby?
7. NUCLEUS - directs the activities of a cell.
Contains genetic information (DNA) in the form of _______________________________
Nucleolus is responsible for the production of ______________________
Pores in the nuclear ___________________ allow RNA to exit nucleus
More analogies : What part of the cell is most like the:
1. Stomach 2. Circulatory System 3. Brain 4. Bones 5. Skin
Human Ear: Structure and Functions (With Diagram)
It comprises a pinna, external auditory meatus (canal) & tympanic membrane.
The pinna is a projecting elastic cartilage covered with skin. Its most prominent outer ridge is called the helix. The lobule is the soft pliable part at its lower end composed of fibrous and adipose tissue richly supplied with blood capillaries. It is sensitive as well as effective in collecting sound waves.
(ii) External Auditory Meatus:
It is a tubular passage supported by cartilage in its exterior part and by bone in its inner part. The meatus (canal) is internally lined by hairy skin (stratified epithelium) and ceruminous glands (wax glands). The latter are modified sweat glands which secrete a waxy substance— the cerumen (ear wax) which prevents the foreign bodies entering the ear.
(iii) The tympanic membrane (tympanum):
Separates the tympanic cavity from the external auditory meatus. It is thin and semi-transparent, almost oval, though somewhat broader above than below. The central part of the tympanic membrane is called the umbo. The handle of the malleus is firmly attached to the membrane’s internal surface.
Functions of External Ear:
It directs sound waves towards the tympanic membrane. The sound waves produce pressure changes over the surface of the tympanic membrane. The cerumen (ear wax) prevents the entry of the foreign bodies into the ear.
2. Middle Ear:
It includes the following:
(i) The tympanic cavity, filled with air is connected with the nasopharynx through the Eustachian tube (auditory tube), which serves to equalize the air pressure in the tym­panic cavity with that on the outside.
(ii) There is a small flexible chain of three small bones called ear ossicles— the malleus (hammer shaped), the incus (anvil shaped) and the stapes (stirrup shaped). The malleus is attached to the tympanic mem­brane on one side and to the incus on the other side.
The incus in turn is connected with the stapes, which is attached to the oval membrane covering the fenestra ovalis (oval window) of the inner ear. Malleus is the largest ossicle, however, stapes is smallest ossicle. Stapes is also the smallest bone in the body.
(iii) Two skeletal muscles, the tensor tympani attached to the malleus and the stapedius attached to the stapes, are also present in the middle ear. Stapedius is the smallest muscle in the body.
(iv) The middle ear is connected with the inner ear through two small openings closed by the membranes. These openings are (a) fenestra ovalis (oval window) as mentioned above and (b) fenestra rotunda (round window).
The fenestra ovalis is covered by foot plate of the stapes. The fenestra rotunda is enclosed by a flexible secondary tympanic membrane. The latter is responsible for equalizing the pressure on either side of the tym­panic membrane.
Functions of Middle ear:
(i) Due to the pressure changes produced by sound waves, the tympanic membrane vibrates, i.e., it moves in and out of the middle ear. Thus the tympanic membrane acts as a resonator that reproduces the vibration of sound,
(ii) It transmits sound waves from external to the internal ear through the chain of ear ossicles,
(iii) The intensity of sound waves is increased about twenty times by the ear ossicles. It may be noted that the frequency of sound does not change and
(iv) From the tympanic cavity extra sound is carried to the pharynx through Eustachian tube.
3. Internal Ear:
There is a body cavity on each side enclosed in the hard periotic bone which contains the perilymph. The later corresponds to the cerebrospinal fluid. A structure, the membranous labyrinth floats in the perilymph. The membranous labyrinth consists of three semicircular ducts, utricle, saccule, endolymphaticus and cochlea.
There are present three semicircular ducts the anterior, the posterior and the lateral semicircular ducts. They arise from the utricle. The anterior and posterior semicircular ducts arise from crus commune.
Each semicircular duct is enlarged at one end to give rise to a small rounded ampulla. The anterior and lateral semicircular ducts bear ampullae at their anterior ends, while the posterior duct contains an ampulla at its posterior end.
Each ampulla contains a sensory patch of cells, the crista Each crista consists of two kinds of cells, the sensory and supporting cells. The sensory cells bear long sensory hairs at their free ends and nerve fibres at the other end. The sensory hairs are partly embedded in a gelatinous mass, the cupula. The cristae are concerned with balance of the body.
(ii) Utricle, Endolymphaticus and Saccule:
The utricle is a dorsally placed structure to which all the three semicircular ducts are connected. The saccule is a ventrally situated structure which is joined with the utricle by a narrow utriculosaccular duct. From this duct a long tube, the ductus endolymphaticus arises which ends blindly as the saccus
endolymphaticus. Both utricle and saccule contain sensory patches, the maculae. A macula comprises sensory and supporting cells similar to those of the crista. The hair are not actually motile and are embedded in a gelatinous membrane, the otolith membrane in which there are also found very small crystals of calcium carbonate, the otolith. The cristae and maculae are the receptors of balance.
Both cristae and maculae are concerned with balance.
It is the main hearing organ which is connected with saccule by a short ductus reuniens leading from the saccule. It is spirally coiled that resembles a snail shell in appearance. It tapers from a broad base to an almost pointed apex.
Internally it consists of three fluid filled chambers or canals, the upper scala vestibuli, lower scala tympani, and the middle scala media (cochlear duct). Both scala vestibuli and scala tympani are filled with perilymph. However scala media is filled with endolymph. Both the scala vestibuli and scala tympani are connected with each other at the apex of the cochlea by a small canal, the helicotrema.
It is important to mention that near the base of the scala vestibuli the wall of the membranous labyrinth comes in contact with the fenestra ovalis, while at the lower end of the scala tympani lies the fenestra rotunda.
The scala media is the most important canal or channel of the cochlea. It bears an upper membrane, the Reissner’s membrane, and lower membrane, basilar membrane. On the basilar membrane a sensory ridge, the organ of Corti is present.
The organ of Corti consists of outer hair cells, inner hair cells, inner pillar cells, outer pillar cells, tunnel of Corti, phalangeal cells (cells of Deiters), cells of Hensen and cells of Claudius.
The sensory hairs project from the outer ends of the hair cells into the scala media, while from the inner end of the cells nerve fibres arise, which unite to form the cochlear nerve. The tectorial membrane overhangs the sensory hair in the scala media. Its properties are to determine the patterns of vibration of sound waves.
Functions of Ear:
The ear performs the functions of hearing and balancing (equilibrium).
1. Mechanism of Hearing:
The sound waves are collected by the external ear up to some extent. They pass through the external auditory meatus to the tympanic membrane which is caused to vibrate. The vibrations are transmitted across the middle ear by the malleus, incus and to the stapes bones. The latter fits into the fenestra ovalis. The perilymph of the internal ear receives the vibrations through the membrane covering, the fenestra ovalis.
From the perilymph the vibrations are transferred to the scala vestibuli of cochlea and then to scala media through Reissner’s membrane. Thereafter, the movements of endolymph and tectorial membrane stimulate the sensory hairs of the organ of Corti.
The impulses thus received by the hair cells are carried to the brain (temporal lobe of each cerebral hemisphere) through the auditory nerve where the sensation of hearing is felt (recognised).
It is evident that the external and middle ears serve to transmit sound waves to the internal ear. It is in the internal ear that the transformation of the vibrations into nerve impulses for relay to the brain takes place. During loud sound, some sound waves are transferred from scala vestibuli to scala tympani through helicotrema.
From scala tympani the sound waves are transmitted to the tympanic or middle ear cavity through the membrane covering the fenestra rotunda. From the tympanic cavity the sound waves are transferred to the pharynx through the Eustachian tube.
The semicircular canals, utricle and saccule of membranous labyrinth are the structures of equilibrium (balancing). Whenever the animal gets tilted or displaced the hair cells of the cristae and maculae are stimulated by the movement of the endolymph and otolith.
The stimulus is carried to the brain through the auditory nerve and the change of the position is detected by the medulla oblongata of the brain. After that, the brain sends impulses (mes­sages) to the muscles to regain the normal conditions.
Spinning or whirling vertigo (dizziness) is characteristic of meniere’s disease.
This is an acute infection of the middle ear caused mainly by bacteria and associated with infection of the nose and throat.
Each cell process is carried out in a specific location in the cell, often located in or around an organelle. Think of an organelle as a level of organization between macromolecules and the cell. Organelles carry out specialized tasks within the cell, localizing functions such as replication, energy production, protein synthesis, and processing of food and waste. The various cells differ in the arrangement and number of organelles, as well as structurally, giving rise to the hundreds of cell types found in the body.
The focus of this section is to understand the organelles of the cell, how they interact with each other, and how they function during transport, growth and division in the cell. You will learn about the controlled chemical environment a cell maintains and what restrictions this places on the types of chemical reactions it can perform. This background is vital to understanding key processes such as how a cell releases energy from glucose, makes and folds proteins, and goes through growth and cell division.
Think of a city and the various jobs within a city. A cell is similar with each organelle serving a specific purpose. There are organelles whose job is to provide shape and structure to the cell, much like the city streets and bridges. These protein rich organelles include intermediate filaments, microtubules, and microfilaments. Some of these actually move other organelles around the cell or change the shape of the cell. When a muscle cell contracts or shortens it does so by the microfilaments made up of the proteins actin and myosin. One special organelle composed of microtubules is located in an area near the nucleus, the centrosome. The centrosome contains a pair called of microtubule bundles known as the centrioles. Centrioles are important because they move chromosomes to opposite ends of the cell during cell replication termed mitosis. Neurons do not have centrioles and cannot replicate.
Other organelles help synthesize the proteins needed by the cell. These protein factories are called ribosomes. They can be scattered within the cell or attached to a membrane channel system called the endoplasmic reticulum or ER. When the ER has ribosomes attached to it, it is termed the rough ER (the ribosomes give it a rough or grainy appearance). When the ER lacks ribosomes it is termed the smooth ER and functions for lipid synthesis and storage of toxins. When a protein is manufactured it must be folded into a specific shape to work. Often additional side chains of carbohydrates must be attached. The protein is processed in the rough ER. Once it is formed it enters the golgi apparatus which is the distributing plant for the cell. It completes any protein processing and then packages it into a vesicle for transport to its destination. Some proteins are needed in the cell membrane and the vesicles make sure they reach the membrane. The golgi apparatus also makes a special type of vesicle termed a lysosome. The lysosome is the garbage man of the cell. It takes in cell debris and waste and destroys it. The lysosome contains very powerful hydrolytic enzymes to accomplish this. It is very important that the enzymes remain in the lysosome or they would destroy the cell.
The power plant of the cell is the mitochondria. This organelle generates the ATP or energy for the cell. Mitochondria even have their own DNA termed mitochondrial DNA (mDNA) and can replicate.
Finally there is the controller of the cell. This is the nucleus. Not all cells have a nucleus and are termed anucleate. If you look at the image of the red blood cells you will see a white dot in the center of the cell – that is where the nucleus used to be. The nucleus is ejected when they mature. Some cells have more than one nucleus and are termed multinucleate. Skeletal muscle cells are very large cells and are multinucleate. The nucleus contains the DNA of the cell and the nucleolus. The nucleolus is an organelle that makes ribosomes. The DNA is your genetic code. It contains the genes that contain the instructions for making every protein in your body. The nucleus is surrounded by it’s own membrane with tiny holes termed nuclear pores. The membrane is called the nuclear membrane or nuclear envelope.
The interactive diagram below shows a drawing of a eukaryotic cell. The cell components in the list link to images that highlight these same structures in a living cell.