ما هي معادلة البناء الضوئي الكيميائية الموزونة؟ What is the balanced equation for photosynthesis?

المعادلة الموزونة هي: 6CO₂ + 6H₂O ➔ C₆H₁₂O₆ + 6O₂ (ستة جزيئات ثاني أكسيد الكربون + ستة جزيئات ماء في وجود طاقة الضوء وصبغة الكلوروفيل تعطي جزيء جلوكوز وستة جزيئات أكسجين). وتتطلب العملية تفاعلات ضوئية لإنتاج ATP و NADPH يعقبها تفاعلات لاضوئية لتثبيت الكربون. [الصيغة الرمزية الموزونة: 6CO₂ + 6H₂O ➔ C₆H₁₂O₆ + 6O₂]

2.2.2Structure and Functions in Living Organisms: Part 1

Animal and Plant Cells: Similarities and Differences

5 min read 9 parts Lesson 4 of 36 1 quiz

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Section 1 of 9Sub-cellular structures

Key Structures of the Respiratory System

Animal cell labelled (nucleus, mitochondria, ribosomes)

Animal cell labelled (nucleus, rough ER, mitochondria)

Structures of animal and plant cells compared

Animal and plant cells are both eukaryotic, so both contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Looking at what each part does lets you explain how a cell is adapted for its job.

Sub-cellular structures

Nucleus

Nucleus holds the DNA as chromosomes, which carry the genes that control cell activity and inheritance.

Cytoplasm

Cytoplasm the site of many chemical reactions, including the first stage of respiration.

Cell membrane

Cell membrane a thin, partially permeable layer that controls the movement of substances in and out.

Mitochondria

Mitochondria release energy from glucose in aerobic respiration. Cells with high energy demands, such as muscle cells, contain many.

Ribosomes

Ribosomes tiny structures that assemble amino acids into proteins following instructions copied from the DNA.

Section 2 of 9Extra structures in plant cells

Plant vacuole showing cell sap and tonoplast

Plasmodesmata — Highways Between Plant Cells (Click-by-Click Lesson)

Plant Cell Vacuole — Interactive Diagram

Plant Cell Biological Drawing — Click-by-Click Animation

Plant cell structures in a micrograph-style view

Plant cells have three additional features that animal cells lack:

Extra structures in plant cells

Cell wall

Cell wall a rigid layer made of cellulose outside the membrane. It strengthens the cell and supports the plant, and it stops the cell bursting when water enters.

Permanent vacuole

Permanent vacuole a large space filled with cell sap (a solution of sugars and salts). It keeps the cell firm and stores substances.

Chloroplasts

Chloroplasts contain the green pigment chlorophyll; they absorb light for photosynthesis. They are found in the green parts of a plant, such as leaf cells, but not in root cells.

Section 3 of 9Comparison table

Structure	Animal cell	Plant cell
Nucleus	Yes	Yes
Cell membrane	Yes	Yes
Mitochondria	Yes	Yes
Ribosomes	Yes	Yes
Cellulose cell wall	No	Yes
Permanent vacuole	No	Yes
Chloroplasts	No	Yes (green parts)

Section 4 of 9Linking structure to function

Examination questions often give an unfamiliar cell and ask you to link a feature to a function.

The method is to name the structure and then state what it does and what that allows the cell to do.

A root hair cell has no chloroplasts because it is underground and receives no light, so photosynthesis cannot occur there.

A leaf palisade cell is packed with chloroplasts so that it can absorb as much light as possible.

A sperm cell contains many mitochondria to supply the energy for swimming.

Notice that in each case the number or presence of a structure reflects the energy or process the cell must carry out.

The cell wall is a favourite exam trap. It is not the same as the cell membrane: the wall is fully permeable and rigid, while the membrane is thin and partially permeable and found in every cell.

Section 5 of 9Studying cells under the microscope

Plant Cell — Light vs Electron Microscope

Plant cell under light vs electron microscope

Plant cell under light microscope vs electron microscope

The nucleus, and in plants the cell wall, vacuole and chloroplasts, can be seen with a light microscope.

Studying cells under the microscope

Mitochondria and ribosomes are too small to see in detail, and need an electron microscope; this is covered in the microscopy lesson.

When drawing a cell, use a sharp pencil, label with ruled lines that do not cross, and draw the outline as a single continuous line.

Section 6 of 9Worked approach to unfamiliar cells

Organelles visible under light vs electron microscope

A reliable way to answer questions about a cell you have never seen is to ask three things in turn.

First, is it eukaryotic?

If a nucleus is visible, it is.

Second, is it plant or animal?

Look for a cell wall, a large vacuole or chloroplasts: if any is present the cell is a plant cell.

Third, what does its unusual feature tell you about its job?

Consider a cell from the lining of the small intestine.

Worked approach to unfamiliar cells

It has many mitochondria and a surface folded into tiny projections.

You would conclude that it carries out a process needing energy, such as absorption by active transport, and that the folds increase surface area.

Consider instead a cell from the middle of a leaf which has a large number of chloroplasts, a cell wall and a big vacuole; it is a plant cell specialised for photosynthesis.

Remember also that some structures can be linked to size. The nucleus is usually the largest organelle in an animal cell, about 10 micrometres across, while mitochondria are about 1 micrometre and ribosomes only around 25 nanometres. This is why a light microscope shows the nucleus clearly but cannot show ribosomes at all.

Finally, do not forget the cytoplasmalthough it looks featureless, it is where many enzyme-controlled reactions happen, and it holds the organelles in position.

Section 7 of 9Exam-style questions

Plant cell labelled (chloroplast, vacuole, cell wall)

Internal Structure of a Leaf and a Palisade Mesophyll Cell

Labelled root hair cell showing organelles

Name the structure in a plant cell that (a) contains chlorophyll, (b) is made of cellulose, (c) contains cell sap. [3]3 marks
Muscle cells contain a large number of mitochondria. Explain why. [2]2 marks
Explain why root hair cells do not contain chloroplasts, but leaf palisade cells do. [3]3 marks

Section 8 of 9Key terms

Term	Meaning
Cell membrane	Thin partially permeable layer that controls what enters and leaves the cell.
Mitochondria	Organelles where aerobic respiration releases energy.
Ribosome	Site of protein synthesis.
Cell wall	Rigid cellulose layer outside the plant cell membrane.
Permanent vacuole	Sap-filled space that keeps a plant cell firm.
Chloroplast	Organelle containing chlorophyll, where photosynthesis occurs.
Chlorophyll	Green pigment that absorbs light energy.

Section 9 of 9Exam technique

Saying the cell wall controls what enters and leaves the cell. That is the job of the cell membrane.

Claiming plant cells do not have mitochondria. They do, because they respire as well as photosynthesise.

Writing that the nucleus 'makes' energy. The mitochondria release energy; the nucleus controls the cell.

Saying chloroplasts are found in all plant cells. Only the cells exposed to light have them.

Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A ⇔ A = I / M ⇔ I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.