Biology
Biology
Cells, genetics, body systems, ecology and evolution — complete biology cheatsheet for A-Level and MDCAT.
01Cell Structure▼
Prokaryotic
No nucleus. Bacteria. 1-10 micrometers.
Eukaryotic
Has nucleus. Plants, animals, fungi.
Animal cell
Nucleus, mitochondria, ribosomes, ER, Golgi, lysosomes.
Plant cell
All animal organelles PLUS cell wall, chloroplasts, large vacuole.
Mitochondria
ATP production. Aerobic respiration. Own DNA.
Chloroplast
Photosynthesis. Thylakoids+stroma. Own DNA. Plants only.
💡
Memory for organelles: Nucleus=control, Mitochondria=power, Ribosome=protein factory, Golgi=post office, Lysosome=recycling bin.
02Cell Division▼
BIOLOGYMitosis vs Meiosis
MITOSIS: 2 identical diploid cells. Growth/repair. Stages: Prophase->Metaphase->Anaphase->Telophase MEIOSIS: 4 haploid gametes. Sexual reproduction. Meiosis I: homologous chromosomes separate Meiosis II: sister chromatids separate Crossing over in Prophase I creates genetic variation.
Mitosis result
2 diploid identical cells
Meiosis result
4 haploid unique cells
Cytokinesis
Cytoplasm divides after telophase
Cancer
Uncontrolled mitosis from mutations
03DNA & Genetics▼
BIOLOGYCentral dogma
DNA --transcription--> mRNA --translation--> Protein Base pairing: A-T (2 H-bonds), G-C (3 H-bonds) Antiparallel strands: 3 to 5 and 5 to 3 Replication (semi-conservative): Helicase unwinds, Primase adds RNA primer, DNA pol III adds nucleotides, Ligase joins fragments
| Term | Definition |
|---|---|
| Gene | DNA sequence coding for a protein |
| Allele | Alternative form of a gene |
| Dominant | Expressed with one copy |
| Recessive | Only expressed when homozygous |
| Codominance | Both alleles expressed (ABO blood) |
| Heterozygous | Two different alleles (Aa) |
04Human Body Systems▼
Circulatory
Heart + blood vessels. Double circulation: pulmonary + systemic.
Respiratory
Gas exchange in alveoli. O2 in, CO2 out by diffusion.
Digestive
Enzymes break food. Villi absorb in small intestine.
Nervous
Brain+spinal cord+neurons. Fast electrical signals.
Endocrine
Glands+hormones. Slower chemical control.
Immune
Phagocytes engulf pathogens. B cells make antibodies.
BIOLOGYHomeostasis
Blood glucose: HIGH -> insulin released -> glucose to glycogen Blood glucose: LOW -> glucagon released -> glycogen to glucose Temperature: HOT -> vasodilation + sweating Temperature: COLD -> vasoconstriction + shivering
05Enzymes▼
Active site
Specific shape. Lock and key model.
Denaturation
High temp or wrong pH changes active site shape permanently.
Competitive inhibitor
Blocks active site. Add more substrate to overcome.
Non-competitive
Binds elsewhere. Changes active site shape. Cannot overcome.
BIOLOGYEnzyme factors
Optimum temp: increase rate to optimum. Above: denature. Optimum pH: each enzyme has specific optimum. Substrate concentration: increases rate to saturation (Vmax). Enzyme concentration: more enzyme -> faster (if substrate excess).
06Ecology & Evolution▼
Food chain
Producer -> Primary -> Secondary -> Tertiary consumer
Energy transfer
~10% passes to next level. ~90% lost as heat.
Carbon cycle
Photosynthesis removes CO2. Respiration+decomposition release it.
Natural selection
Variation -> Competition -> Survival -> Reproduction -> Evolution
BIOLOGYClassification
Domain -> Kingdom -> Phylum -> Class -> Order -> Family -> Genus -> Species Memory: Dear King Philip Came Over For Good Soup
❓ Quiz
What is the result of meiosis?
Meiosis produces 4 genetically unique haploid gametes. Crossing over in Prophase I ensures genetic variation.