Is the inside of a cell just empty water? No. The space outside the nucleus and inside the cell membrane is where much of the cell's work gets done. Threaded through it is a net-like framework. In this note you will meet both: the cytoplasm and the endoplasmic reticulum.
1. The cytoplasm and its many names
The part of the protoplasm that lies outside the nucleus and inside the cell membrane is the cytoplasm. It is made of two things: the matrix and the organelles.
The cytoplasmic matrix is the ground substance of the cytoplasm: a semifluid, granular, translucent, homogeneous colloidal fluid. It goes by two more names, hyaloplasm and cytosol. H. A. Lardy first used the word cytosol, in 1965.
The cytoplasm itself has two zones. The dense, less granular, rigid outer zone is the ectoplasm, also called the cortex or plasmagel. The less dense central zone is the endoplasm.
Four words and four meanings. Pick up a meaning, then drop it in the box of the right word.
match themmeaning, then word
Word and meaning
Pick up a meaning, then drop it in its word's box.
Right. Next one.
Not yet. Ask which is a name for the matrix, which is the outer zone and which is the inner zone.
All in place. The matrix has two names, hyaloplasm and cytosol. The zones are the ectoplasm outside and the endoplasm inside.
2. What the cytoplasm holds and does
The inorganic part is mainly water, dissolved gases, minerals and ions. The organic part is carbohydrates, organic acids, lipids, proteins, nucleic acids, hormones, vitamins and pigments. Water alone makes up 65-96%.
The cytoplasm does six jobs: it holds the organelles, carries out some biological work, controls the acidity and alkalinity of the cell, helps remove wastes, responds to stimuli, and helps absorb water.
Glycolysis, the first stage of respiration, happens right here in the cytoplasm. And since the cytoplasm is the store of enzymes, it indirectly controls all metabolism.
3. The endoplasmic reticulum
The net-like arrangement seen in the cytoplasm of a mature cell is the endoplasmic reticulum (ER). Keith R. Porter and colleagues (Claude and Fullam) discovered it in liver cells in 1945. It was named in 1953.
The ER arises from cytoplasmic membrane, nuclear membrane or cell membrane. Most eukaryotic cells have it, but cells of the liver, pancreas and endocrine glands have more.
The ER is of two kinds. With ribosomes attached it is rough (granular) ER; without them it is smooth (agranular) ER.
Structurally the ER comes in three forms. Cisternae are flat, unbranched, long tank-like sacs of 40-50 millimicron. Vesicles are round, 25-50 millimicron. Tubules are tube-like, 50-190 millimicron, and usually carry no ribosomes.
The ER is mainly protein (60-70%) and lipid (30-40%). It holds about 32 kinds of enzyme, such as glucose 6-phosphatase, active ATPase and NADH diaphorase.
Now tap the eight points on the drawing, made after Figure 1.10, and learn the parts.
Figure 1.10tap a point
Know the parts of the ER
Smooth ER. No ribosomes on it, so it is agranular.
Rough ER. Ribosomes are attached, so it is granular.
Cisternae. Flat, unbranched, long tanks of 40-50 millimicron.
Intercisternal connection. In the figure, the link that joins one cisterna to the next.
Membrane. The ER is bounded by membrane. Its substance is mainly protein and lipid.
Ribosome. Sits on the surface of rough ER. The ER is a carrier of ribosomes.
Vesicle. A round sac of 25-50 millimicron.
Tubule. Tube-like, 50-190 millimicron. Usually without ribosomes.
All eight seen. Notice that having ribosomes or not is what separates rough from smooth ER.
Drawn by hand after the book's figure, not to scale.
4. Smooth versus rough ER
The small broken-off pieces of rough ER are called microsomes.
Jobs of the ER: it is a framework for the protoplasm, rough ER makes protein, smooth ER makes lipid (some say hormones and glycogen too), it transports lipid and protein, it carries ribosomes, and it detoxifies poisons.
The difference in one line: rough ER carries ribosomes and makes protein. Smooth ER carries no ribosomes and makes no protein, but it can make lipid or hormones.
Eight chips. For each, decide whether it describes smooth ER or rough ER.
sort themtap a chip, then pick a bin
Smooth or rough?
Pick up a chip, then drop it in a bin. One question decides it: are ribosomes there?
Right. Next one.
Not yet. Think: granules are ribosomes, and ribosomes are what make it rough.
All in place. Ribosomes do protein work, so granular rough ER makes protein. Smooth ER is agranular and can make lipid or hormones.
5. Check yourself
Three questions in the exam's style. Start with the first.
check yourselfpick one answer
Question 1
The functions of the endoplasmic reticulum are:
i. Giving a framework to the cytoplasm ii. Protein is made on the rough ER iii. Helping mitochondria make ATP
Right. i and ii are right: the ER is a framework of the protoplasm and protein is made on the rough ER; iii is wrong, since ATP is made by the mitochondria.
i is right, but iii is wrong: helping make ATP is not an ER job, the mitochondria make ATP.
ii is right, but iii is wrong: the ER does not help the mitochondria make ATP.
Not all three, because helping make ATP is not a function of the ER.
Now the second.
check yourselfpick one answer
Question 2
By what other name is the cytoplasm known?
There is no term called Cystol.
Right. The fluid part of the cytoplasm is called cytosol.
Cytomembrane points to the cell membrane, not to the cytoplasm.
There is no term called Cytocyst.
And the last one.
check yourselfpick one answer
Question 3
Which regulates the acidity and alkalinity of the cell?
The cell wall is a non-living layer and does not regulate pH.
Right. The cytoplasm regulates the acidity and alkalinity of the cell.
The cell membrane controls movement of substances, not pH.
The ER takes part in making and carrying protein and lipid.
The whole note on eight cards.
cut from the notetap to turn over
Eight cards
QuestionWhat is the cytoplasm and what is it made of?
AnswerThe part of protoplasm outside the nucleus and inside the cell membrane; it is made of matrix and organelles.
QuestionHow do ectoplasm and endoplasm differ?
AnswerEctoplasm: dense, less granular outer rigid zone (cortex, plasmagel). Endoplasm: less dense central zone.
QuestionWhich stage of respiration occurs in the cytoplasm? Why is the cytoplasm called the controller of metabolism?
AnswerGlycolysis, the first stage. Because it stores the enzymes that control all biochemical reactions.
QuestionWhat is the ER? Who discovered it, and when?
AnswerThe network in the cytoplasm. Keith R. Porter and colleagues, in 1945, in liver cells.
QuestionHow are rough and smooth ER told apart?
AnswerRough (granular) if ribosomes are attached; smooth (agranular) if not.
QuestionHow many structural kinds of ER are there? Which usually lacks ribosomes?
AnswerThree: cisternae, vesicles, tubules. Tubules usually lack ribosomes.
QuestionThe small broken-off pieces of rough ER are called ….
AnswerMicrosomes come from rough ER, not smooth ER.
QuestionWhat does rough ER do that smooth ER does not?
AnswerRough ER holds ribosomes and makes protein. Smooth ER does not make protein; it makes lipid or hormones.
Source: Biology 1st Paper (Botany), Classes 11-12 (NCTB), Chapter 1 “Cell and Its Structure”, section 1.3.