Grade 8 Science: Cells, Tissues, Organs, and Systems

Flashcards covering Grade 8 science concepts including cell theory, characteristics of living things, light and electron microscopy, plant vs. animal cell organelles, membrane transport, diffusion, and unit design challenges.

What are the required organelles and criteria for the Cells Design Project?

Students must build a 2D poster/digital diagram or 3D model representing a plant or animal cell with all functional organelles proportionate and labelled, explain their functions and connections in a presentation, and hand in an explanatory key. Required organelles include: cell membrane, mitochondria, nucleus, vacuole(s), ribosomes, golgi body, cytoplasm, endoplasmic reticulum, and for plant cells only, cell wall and chloroplast.

What is the due date and mark breakdown for the Cells Design Project?

The due date is November 12, 2026. The rubric awards up to $30$ total marks: Organelles needed for function presented and labelled ($10$ marks), Organelle functions/connections fully explained ($10$ marks), Creativity and effort ($5$ marks), and Presentation ($5$ marks).

What are the two foundational statements of the cell theory?

1. All living things are composed of cells.
2. All cells come from pre-existing cells.

What are the six characteristics of living things?

1. Living things are composed of cells.
2. Living things reproduce, grow, and repair themselves.
3. Living things require energy.
4. Living things respond to the environment.
5. Living things have a life span.
6. Living things produce wastes.

Why is a volcano not classified as a living organism even though lava moves, the volcano gets larger, and gases burst from its top?

Before something can be classified as an organism, it must show all of the characteristics of living things. Non-living things such as volcanoes only show some of these characteristics.

What procedure is followed in "The Apple Juice Test" to compare living and non-living materials?

Equal amounts ($25\,\text{mL}$) of sand and dry yeast are added to separate containers ($250\text{-mL}$ beakers or glasses) filled with equal amounts of apple juice to observe differences in activity between living and non-living substances.

What are the specific functions of the cell nucleus and chromosomes?

The nucleus is the control centre that directs all cell activities. Chromosomes are located inside the nucleus and contain genetic information that holds the "construction plans" for all pieces of the cell.

What are the roles of the cell membrane and cytoplasm?

The cell membrane acts as a gatekeeper controlling the movement of nutrients and waste into and out of the cell. The cytoplasm is a watery fluid allowing materials to transport quickly between cell structures while storing wastes until disposal.

How does the vacuole differ between plant cells and animal cells?

In both cells, vacuoles store water and nutrients such as sugar and minerals; however, in a plant cell, the vacuole takes up a much larger part of the cytoplasm than in an animal cell.

What two structures are unique to plant cells, and what are their functions?

1. Cell Wall: Protects and supports the plant cell, with pores allowing gases, water, and minerals to pass.
2. Chloroplasts: Contain chlorophyll molecules that use sunlight to manufacture food for the plant cell.

Identify the seven numbered structures in this diagram of a plant cell.

1: nucleus 2: chromosomes 3: cell membrane 4: cytoplasm 5: vacuole 6: cell wall 7: chloroplast

What are the two specialised cellular structures for movement, and how do they function?

1. Flagellum: A whiplike tail that helps some cells move.
2. Cilia: Tiny hairs that work together to move a cell or move the environment surrounding the cell.

How did Anton van Leeuwenhoek's early microscope differ from compound light microscopes?

Anton van Leeuwenhoek's microscopes in the 1660s used a single lens mounted between two brass plates to magnify objects $10\times$ or more. Compound light microscopes introduced a second lens; an image magnified $10\times$ by the first lens and $10\times$ by the second lens is magnified $100\times$.

What optical limitation prevents compound light microscopes from magnifying beyond approximately $2000\times$?

To make images larger, glass lenses must become thicker. As glass lenses become thicker, the light image blurs until no detail can be distinguished.

What magnification can a Transmission Electron Microscope (TEM) achieve, and what are its two major limitations?

A TEM achieves up to $2\,000\,000\times$ magnification using electron beams. Its limitations are: 1. Specimens must be cut into very thin slices encased in plastic because electrons are easily absorbed or deflected by thick specimens. 2. Encasing cells in plastic kills them, meaning only dead cells can be observed.

How does a Scanning Electron Microscope (SEM) operate compared to a Transmission Electron Microscope (TEM)?

An SEM uses electrons reflected off the specimen to build a digital 3D image. Specimen thickness does not matter, but only the outer surface can be observed, and its magnification is lower than that of a TEM.

What is the function of mitochondria in the cell, and what chemical process occurs inside them?

Mitochondria act as the cell's "powerhouse" by releasing energy through cellular respiration, combining sugar molecules with oxygen to form carbon dioxide and water.

What are the cellular roles of ribosomes and the endoplasmic reticulum?

Ribosomes put together large protein molecules needed for cell growth, repair, and reproduction using information from the nucleus. The endoplasmic reticulum is a series of folded membranes transporting materials through the cytoplasm; it appears "rough" when ribosomes are attached.

What is the function of the Golgi apparatus?

Discovered by Camillo Golgi, the Golgi apparatus stores proteins and packages them into vesicles, which transport the protein molecules to the surface of the cell to be released outside.

Why are lysosomes called "suicide sacs," and what is their role in cell recycling and defense?

Lysosomes patrol the cytoplasm containing special proteins that break down large molecules into reusable building blocks, and they destroy invading organisms in animals. They are called "suicide sacs" because damaged or worn-out cells are destroyed by their own lysosomes.

What is the structural composition of the cell membrane?

The cell membrane is composed of two layers of fat (lipids) embedded with protein molecules and protein-lined pores of several different sizes.

What do the terms permeable, impermeable, and selectively permeable mean?

Permeable means permitting the passage of materials; impermeable means not permitting passage; selectively permeable means permitting certain substances to pass through while preventing others.

What is diffusion, and how does it drive gas exchange across cell membranes?

Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration resulting from random molecular collisions. Used substances like oxygen are in lower concentration inside the cell, causing oxygen to diffuse inward, while waste carbon dioxide is more concentrated inside and diffuses outward.

How does insulin regulate sugar entry through cell membrane pores?

Insulin is a protein released into the blood by the pancreas that acts like a key to a lock; it binds to receptors on the cell membrane, triggering specific pores to open so sugar can enter the cell.

In this membrane permeability experiment using glass, wire/plastic mesh, and cloth, how does permeability vary among the coverings?

Glass is impermeable to all three substances (water, sugar, sugar-water solution); mesh is permeable to all three substances; cloth is selectively permeable, allowing water through while blocking larger dry sugar granules.

What are the three specialized cell options provided for the Unit 1 Design Challenge?

1. A Cell That Carries Oxygen: Design and build a simulation of a red blood cell that carries oxygen to other cells.
2. A Cell That Removes Dirt: Design and build a model of a cell that could remove dirt from the lung.
3. Artificial Skin: Design and build a model of skin that will protect other cells.