Cell membranes, transport mechanisms, organelles, the cell cycle, and cell division.
Active transport moves substances against their concentration or electrochemical gradients using cellular energy, while passive transport moves them down those gradients without energy input. Understanding the role of gradients and the types of each transport mechanism clarifies how cells regulate nutrients, ions, and waste.
Mitosis is a four‑stage process—prophase, metaphase, anaphase, and telophase—that divides a diploid nucleus into two genetically identical nuclei, followed by cytokinesis that splits the cytoplasm. Labeled diagrams of each stage make the chromosome movements and spindle dynamics easy to visualise.
Transcription copies DNA information into messenger RNA inside the nucleus, while translation reads that mRNA to assemble a protein on ribosomes in the cytoplasm. Together they constitute the two main stages of gene expression that turn genetic blueprints into functional molecules.
In an isotonic solution a cell keeps its normal size because water moves in and out at equal rates. In a hypotonic solution water enters the cell, causing it to swell and possibly burst. In a hypertonic solution water leaves the cell, making it shrink or crenate.
Endocytosis and exocytosis are opposite, energy‑requiring processes that let cells transport macromolecules and particles across the plasma membrane. Endocytosis brings material into the cell by forming a vesicle, while exocytosis expels material by fusing a vesicle with the membrane.
Interphase is the preparatory stage of the cell cycle, occupying about 90 % of a cell’s lifetime. It consists of three sequential phases—G1, S, and G2—during which the cell grows, copies its DNA, and readies the machinery needed for mitosis.
Simple diffusion and facilitated diffusion are both passive transport processes that move substances down their concentration gradient without using cellular energy. Simple diffusion lets small, non‑polar molecules slip directly through the lipid bilayer, while facilitated diffusion relies on membrane proteins to carry larger or polar molecules across the membrane.
A chromosome is a single DNA‑protein structure; a chromatid is one half of a duplicated chromosome. In cell‑division drawings you count each chromosome once, even when it appears as two sister chromatids. This guide explains the visual cues that tell you when you are looking at a chromosome, a chromatid, or a pair of sister chromatids, and shows how to correctly count them.
Diffusion is the passive movement of any particles from an area of higher concentration to lower concentration, while osmosis is the passive movement of water specifically across a semi‑permeable membrane from a region of higher water potential to lower water potential. Both rely on concentration gradients, but only osmosis requires a membrane that blocks solutes but lets water pass.
A concentration gradient describes how the amount of a substance changes from one location to another. It is the driving force behind diffusion, osmosis, and many cellular energy‑producing processes.