OCR A Level biology Cell structure

Eukaryotic cells

Larger than prokaryotic cells and their DNA is contained in a nucleus.

Prokaryotic cells

Smaller cells that do not have a nucleus.

Organ systems

Made up of a range of organs working together to perform a function.

Organs

Made up of a range of tissues working together to perform a function.

Tissues

Specialized cells of a similar structure and function organized into groups.

Cell-surface membrane

Phospholipid bilayer with proteins and cholesterol embedded within it; involved in transport and cell recognition.

Fluid-mosaic model

Describes the fluidity and range of molecules in the cell membrane.

Nucleus

Surrounded by a double membrane nuclear envelope; contains chromosomes and is the site of DNA replication and transcription.

Nucleolus

Site of rRNA production and makes ribosomes.

Mitochondria

Double membrane organelle; site of aerobic respiration and ATP production.

Chloroplasts

Surrounded by a double membrane; site of photosynthesis.

Thylakoids

Folded membranes in chloroplasts containing chlorophyll pigments.

Golgi apparatus

Stacks of membranes that modify proteins and lipids and transport finished products in Golgi vesicles.

Lysosomes

Type of Golgi vesicle that releases lysozymes; formed when the Golgi apparatus contains hydrolytic enzymes.

Ribosomes

Small granules made of protein and rRNA; site of translation in protein synthesis.

Rough endoplasmic reticulum (RER)

Sheets of membranes linked to the nucleus; site of protein and glycoprotein synthesis.

Smooth endoplasmic reticulum (SER)

Creates, stores, and transports lipids and carbohydrates.

Cell wall

Found in plants, algae, and fungi; provides structural strength to cells.

Middle lamella

Thin boundary layer between adjacent cells in plants.

Cell Vacuole

A single membrane sac found in plants, filled with fluid containing salts, sugars, and amino acids, providing support, storing amino acids and sugars, and can contain pigments to attract pollinators.

Tonoplast

The membrane surrounding a cell vacuole.

Cytoskeleton

A structure found within the cytoplasm that provides mechanical strength to cells, helps with transport within cells, and allows cell movement.

Cilia

Cellular structures with 2 central microtubules in a 9+2 arrangement that move in a beating motion.

Protein Production

The process where proteins are synthesized on ribosomes bound to the RER, packaged into transport vesicles, and modified in the Golgi apparatus before being released.

DNA in Prokaryotic Cells

Found as a single, circular molecule in the cytoplasm, not associated with histone proteins.

Cell Wall in Prokaryotic Cells

Made of a glycoprotein called murein or peptidoglycan, and does not contain cellulose or chitin.

Plasmids

Rings of DNA in some bacteria containing genes linked to survival, such as antibiotic resistance.

Capsule

A protective layer surrounding the cell wall in some bacteria that helps them stick together.

Flagella

Structures used by some bacteria for locomotion.

Microscopes

Tools that have enabled the study of the internal structure of cells.

Differential Staining

A technique involving the use of multiple chemical stains to color different structures of cells for better visibility.

Application of Differential Staining

Used in medicine to detect abnormalities in the proportion of different white blood cells in a patient's blood sample.

Gram Staining

A method to visualize different bacteria using two stains, crystal violet and Fuchsin/Safranin, to differentiate Gram-positive and Gram-negative bacteria.

Gram-positive Bacteria

Bacteria that have thicker cell walls and retain the crystal violet stain during Gram staining.

Gram-negative Bacteria

Bacteria that have thinner cell walls and do not retain the crystal violet stain, appearing pink after Gram staining.

Microscope magnification

Refers to how many times larger the image is compared to the object.

Microscope resolution

The minimum distance between two objects in which they can still be viewed as separate.

Optical microscope

A type of microscope that uses light to view samples, having poor resolution due to the long wavelength of light.

Scientific drawings

Drawings that follow specific rules to represent observed structures from under a microscope, such as drawing in pencil and annotating components.

Electron microscope (EM)

A type of microscope that uses a beam of electrons to create high-resolution images, capable of visualizing small organelles.

Transmission Electron Microscope (TEM)

An electron microscope where extremely thin specimens are stained and placed in a vacuum, producing 2D images of internal structures.

Scanning Electron Microscope (SEM)

An electron microscope that beams electrons onto the surface of specimens, producing 3D images without the need for thin specimens.

Laser scanning confocal microscope

Uses a focused laser beam to scan a fluorescently stained specimen point-by-point, creating a high-resolution, high-contrast 2D image.

Peptidoglycan cell wall

A structural component of bacterial cell walls that determines whether bacteria are Gram-positive or Gram-negative.

WBC with lobed nucleus

White blood cells that can be stained and observed under a microscope, often in conjunction with bacterial staining.

Formula for magnification

Magnification = size of image / size of real object.

Vacuum in electron microscopy

A necessary condition for examining samples in electron microscopes, as electrons are absorbed by air.

Black and white images in EM

Images produced by electron microscopes that must be stained, resulting in monochrome visuals.

3D imaging in SEM

The result of scattering electrons off the surface of specimens, allowing for three-dimensional visualization.

Detailed images in TEM

Images that show the internal structure of cells in two dimensions, highlighting areas that absorb electrons.

High-resolution imaging

The ability to visualize small details in specimens, achieved through electron microscopy due to short wavelengths of electrons.

Fluorescent staining

A technique used in laser scanning confocal microscopy to enhance the visibility of specific structures in specimens.

Solid lines in scientific drawings

A rule for scientific drawings that specifies using solid lines without overlapping to accurately represent structures.

Non-living specimens in EM

Samples that can be examined using electron microscopes, as living specimens cannot be used due to vacuum requirements.

Color images in optical microscopy

Images obtained from optical microscopes that allow for the examination of living samples.