3.2.1 Cell structure for A-Level Biology (AQA)

Which structure forms the boundary of the cell and controls the movement of substances into and out of the cytoplasm?

Cell-surface membrane

A selectively permeable phospholipid bilayer containing proteins for transport and signalling.

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Which organelle contains the genetic material organised into linear chromosomes?

Nucleus

Surrounded by a double membrane (nuclear envelope) and controls many cell activities.

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Which structure inside the nucleus produces ribosomes?

Nucleolus

A dense region where rRNA is produced and ribosome subunits are assembled.

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Which organelle is the main site of aerobic respiration and ATP production in eukaryotic cells?

Mitochondrion

Contains folded inner membranes called cristae that increase surface area for respiration.

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Which organelle carries out photosynthesis in plant and algal cells?

Chloroplast

Contains chlorophyll and internal thylakoid membranes where light-dependent reactions occur.

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Which organelle modifies, sorts and packages proteins into vesicles for transport?

Golgi apparatus

Receives proteins from the ER and prepares them for secretion or use in the cell.

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Which small vesicle contains digestive enzymes used to break down unwanted materials or pathogens?

Lysosome

A vesicle that releases hydrolytic enzymes.

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Which cellular structure is responsible for protein synthesis?

Ribosome

Can be free in the cytoplasm or attached to rough ER.

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Which membranous network studded with ribosomes transports and folds newly made proteins?

Rough endoplasmic reticulum

Proteins made here are usually destined for secretion or membranes.

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Which membranous network without ribosomes is involved in lipid synthesis and detoxification?

Smooth endoplasmic reticulum

Also plays roles in carbohydrate metabolism and calcium storage.

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Which rigid outer layer provides structural support in plant, algal and fungal cells?

Cell wall

In plants it is composed of cellulose.

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Which large fluid-filled compartment maintains turgor pressure in plant cells?

Cell vacuole

Surrounded by the tonoplast and filled with cell sap.

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True or False:

Chloroplasts are found in both plant and animal cells.

False

Chloroplasts occur in plants and algae but not in animal cells.

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True or False:

Ribosomes may be found attached to the rough endoplasmic reticulum.

True

Attached ribosomes synthesise proteins destined for secretion or membranes.

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True or False:

Lysosomes are formed from vesicles produced by the Golgi apparatus.

True

These vesicles are distinct organelles which contain hydrolytic enzymes for digestion.

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True or False:

The smooth endoplasmic reticulum is mainly responsible for protein synthesis.

False

Protein synthesis occurs on ribosomes, including those on rough ER.

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Fill in the blank:

In multicellular organisms, specialised cells form ______, which combine to form organs.

tissues

Organisation hierarchy: cells → tissues → organs → organ systems.

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Fill in the blank:

The folded inner membrane of the mitochondrion that increases surface area is called the ______.

cristae

Cristae contain proteins involved in oxidative phosphorylation.

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Fill in the blank:

The fluid inside the plant cell vacuole is known as ______.

cell sap

Contains water, ions, sugars and pigments that help maintain osmotic balance.

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How does the typical size of prokaryotic cells compare with eukaryotic cells?

Smaller

Prokaryotic cells are generally much smaller than eukaryotic cells, which affects their surface area to volume ratio.

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What type of cellular structures are absent from the cytoplasm of prokaryotic cells?

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Membrane-bound organelles

Prokaryotic cytoplasm does not contain structures such as mitochondria or endoplasmic reticulum.

How do ribosomes in prokaryotic cells compare in size to those in eukaryotic cells?

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Smaller ribosomes

Prokaryotic ribosomes are typically 70S, whereas eukaryotic ribosomes are 80S.

What form does the main genetic material take inside a prokaryotic cell?

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Single circular DNA molecule

This DNA is free in the cytoplasm and not enclosed within a nucleus.

Fill in the blanks:

In prokaryotic cells, the main DNA molecule is free in the cytoplasm and is not associated with ______ ______.

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Histone proteins

In contrast, eukaryotic DNA is associated with histone proteins.

What substance forms the **main structural component** of the **prokaryotic cell wall**?

Murein ## Footnote Murein is a glycoprotein also called peptidoglycan.

# True or False: **Prokaryotic cells** contain a **membrane-bound nucleus**.

False ## Footnote Instead of a nucleus, their DNA lies free in the cytoplasm.

What **small, circular DNA molecules** may also be present in many **prokaryotic cells**?

Plasmids ## Footnote Plasmids often carry genes that may provide advantages such as antibiotic resistance.

What **protective outer layer** may surround some **prokaryotic cells** outside the cell wall?

Capsule ## Footnote Capsules can help protect bacteria from immune responses or desiccation.

What **structures** allow some **prokaryotic cells** to move through liquid environments?

Flagella ## Footnote Flagella are long protein filaments that rotate to produce movement.

# True or False: **All prokaryotic cells** contain **plasmids and flagella**.

False ## Footnote These structures are present in many, but not all, prokaryotes.

What term describes **infectious particles** that are **acellular and non-living**?

Viruses ## Footnote Viruses cannot carry out metabolic processes independently.

# Fill in the blank: The **protein coat** that surrounds **viral genetic material** is called the \_\_\_\_\_\_.

Capsid ## Footnote The capsid protects the viral nucleic acid and helps determine virus shape.

What **viral structure** enables a virus to **recognise and bind to host cells**?

Attachment protein ## Footnote Attachment proteins bind to complementary receptors on host cell membranes.

# True or False: **Viruses** contain **cytoplasm and ribosomes** for protein synthesis.

False ## Footnote Viruses rely entirely on host cells to replicate and produce proteins.

Why are **transmission electron microscopes** able to reveal much smaller cell structures than **optical microscopes**?

They have higher resolution. ## Footnote Electron beams have a much shorter wavelength than visible light, allowing finer detail to be distinguished.

What limitation of **optical microscopes** restricts the level of **cellular detail** that can be observed?

Low resolution ## Footnote The resolving power is limited by the wavelength of visible light (~200 nm resolution limit).

Which type of microscope produces detailed images of the **internal ultrastructure** of cells by passing **electrons through a thin specimen**?

Transmission electron microscope ## Footnote Often abbreviated as TEM; used to study organelles and internal cell structures.

Which type of electron microscope produces detailed **three-dimensional images** of the **surface of cells and tissues**?

Scanning electron microscope ## Footnote SEM scans the specimen surface with electrons to produce 3D-like surface images.

What term describes how much larger an image appears compared with the **real object** in **microscopy**?

Magnification ## Footnote Magnification does not necessarily mean more detail is visible.

What term describes the **ability to distinguish** two **separate points** that are close together?

Resolution ## Footnote Higher resolution means two nearby points can be seen as separate.

Why can increasing **magnification** without improving **resolution** fail to show more cellular detail?

Resolution limit ## Footnote The image becomes larger but remains blurred if the resolving power is unchanged.

# Fill in the blank: The formula used to calculate **microscope magnification** is: magnification = size of image ÷ \_\_\_\_\_\_.

size of real object ## Footnote Rearranging the equation allows calculation of real object size from image measurements.

When measuring the **size of a cell** from a microscope image, what must be known or calculated first?

Magnification ## Footnote Real size = image size ÷ magnification.

# True or False: **Scanning electron microscopes** are mainly used to observe the **internal structures of organelles**.

False ## Footnote Internal ultrastructure is typically studied using TEM rather than SEM.

What laboratory technique is used to **separate different components of cells** after they have been **broken open**?

Cell fractionation ## Footnote The process isolates organelles so they can be studied individually.

What process spins **cell fractions** at **extremely high speeds** to separate organelles based on mass and density?

Ultracentrifugation ## Footnote Heavier components sediment first during high-speed centrifugation.

What is the first major step in **cell fractionation** before organelles are separated by **centrifugation**?

Homogenisation ## Footnote Cells are broken open in a cold, isotonic, buffered solution.

Why is a **cold solution** used during the **homogenisation step** of cell fractionation?

It prevents enzyme activity. ## Footnote Low temperature slows enzyme reactions that could damage organelles.

Why is the **homogenisation solution** **isotonic** during cell fractionation?

It prevents osmotic damage. ## Footnote Isotonic conditions prevent organelles swelling or shrinking.

# True or False: Early **microscopists** immediately recognised all structures seen under **electron microscopes** as true organelles.

False ## Footnote Scientists initially debated whether some observed structures were artefacts produced during preparation.

What term describes **structures seen under microscopes** that are produced by **preparation or staining** rather than actually existing in the cell?

Artefacts ## Footnote Distinguishing artefacts from genuine organelles took time in microscopy research.

What chemical solution can be used to test for **starch grains** in **plant cells** under a microscope?

Iodine in potassium iodide ## Footnote Starch turns blue-black when iodine solution is applied.

3.2.1 Cell structure Flashcards

Identify the structure and function of eukaryotic and prokaryotic cell components and relate them to cellular specialization. (52 cards)