science

Suction pressure

Suction pressure is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Suction pressure rather than just read about it. In short: Suction pressure is also called Diffusion Pressure Deficit. If some solute is dissolved in solvent, its diffusion pressure decreases.

Key takeaways

Suction pressure belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Suction pressure to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Suction pressure from memory before moving on to harder problems.

Reference excerpt

Suction pressure is also called Diffusion Pressure Deficit. If some solute is dissolved in solvent, its diffusion pressure decreases. The difference between diffusion pressure of pure solvent and solution is called diffusion pressure deficit (DPD). It is a reduction in the diffusion pressure of solvent in the solution over its pure state due to the presence of solutes in it and forces opposing diffusion. When a plant cell is placed in a hypotonic solution, water enters into a cell by endosmosis and as a result turgor pressure (TP) develops in the cell. The cell membrane becomes stretched and the osmotic pressure (OP) of the cell decreases. As the cell absorbs more and more water its turgor pressure increases and osmotic pressure decreases. When a cell is fully turgid, its OP is equal to TP and DPD is zero. Turgid cells cannot absorb any more water. Thus, with reference to plant cells, the DPD can be described as the actual thirst of a cell for water and can be expressed as :

D P D = O P − T P {\displaystyle DPD=OP-TP}

Thus it is DPD that tends to equate and represents the water-absorbing ability of a cell, it is also called suction force (SF) or suction pressure (SP). The actual pressure with which a cell absorbs water is called "suction pressure".

Factors affecting DPD DPD is directly proportional to the height of the plant, tree or organism. DPD is governed by two factors i.e. turgor pressure and osmotic pressure. Turgor pressure can be denoted as wall pressure in some cases. DPD is directly proportional to the concentration of the solution. DPD decreases with dilution of the solution.

History The term diffusion pressure deficit (DPD) was coined by B.S. Meyer in 1938. Originally DPD was described as suction pressure by German botanist Otto Renner in 1915.

Refrigeration In refrigeration and air conditioning systems, the suction pressure' (also called the low-side pressure) is the intake pressure generated by the system compressor while operating. The suction pressure, along with the suction temperature the wet bulb temperature of the discharge air are used to determine the correct refrigerant charge in a system.

Further reading The measurement of Diffusion Pressure Deficit in plants by the method of Vapour Equilibrium (By R. O. SLATYER, 1958)

References

Worked examples

Example 1 — a first encounter with Suction pressure

Start with the simplest possible case. Write down what Suction pressure claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Suction pressure before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Suction pressure ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Suction pressure

In research: Suction pressure appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Suction pressure in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Suction pressure is common in secondary-school and first-year university syllabi. It links to neighbouring topics Diffusion, so understanding it makes those chapters shorter.
In everyday life: Look for Suction pressure outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Suction pressure in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Suction pressure means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Suction pressure out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Suction pressure in simple terms?

Suction pressure is also called Diffusion Pressure Deficit. If some solute is dissolved in solvent, its diffusion pressure decreases.

Why does Suction pressure matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Suction pressure?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Suction pressure.