Unlock in-depth, carefully crafted biology notes, for all topics. Written according to the 2023/2024 syllabus. References include trustworthy and reliable websites; savemyexams & online cambridge textbooks.
Chapter 1: Characteristics & Classification of living organisms:
1.1 Characteristics of all living organisms:
MRS GREN:
● Movement:
An action by an organism or part of an organism causing a change of position or place (
all living organisms move )
- EG. Plants: Move leaf towards sunlight, etc
Animals: Wagging a tail, walking, etc
● Respiration:
The chemical reactions that break down nutrient molecules in living cells to release
energy for metabolism
- Types of respiration:
Aerobic Respiration: (w/ oxygen)
Glucose + Oxygen ------> Carbon Dioxide + Water
Anaerobic Respiration: (w/o oxygen)
1. In animal cells:
2. In yeast cells:
IGCSE Biology Notes 2023/2024 Yvonne Cheong
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● Sensitivity:
The ability to detect or sense stimuli in the internal or external environment and to make
appropriate responses
EG. The plant detects the direction of sunlight and grows towards it.
● Growth:
A permanent increase in size and dry mass by an increase in cell number or cell size or
both (All organisms grow)
● Reproduction:
The processes that make more of the same kind of organism/species.
- Types of reproduction:
Sexual Reproduction:
Reproduction between two parents; a male and female organism, offspring has variations
based on parents and their DNA.
Asexual Reproduction:
Reproduction with only one parent, offspring are genetically identical to parents
Common in the plant world.
● Excretion:
The removal of toxic materials from organisms. The waste
products of metabolism (chemical reactions in cells including
respiration) and substances in excess of requirements.
- EG. Removal of Carbon dioxide from the body, as it is a
waste product of respiration.
------------------
Other excreted materials include: Urea, Water, Urine
Not to be confused with egestion (passing out of
undigested food through the anus)
● Nutrition:
The taking in of materials for energy, growth, and development; plants require light,
carbon dioxide, water, and ions; animals need organic compounds, and ions and usually
need water
IGCSE Biology Notes 2023/2024 Yvonne Cheong
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1.2 Concept & Uses of Classification Systems
Definitions:
Organism- a living thing (lol)
Species- a group of organisms that can reproduce to produce fertile offspring
Binomial Naming System:
- A system of naming system which includes two parts: genus and species:
EG.
Common name: Scientific name:
Tiger
Genus Species
Panthera tigris
- Genus is always first and starts with a Capital letter, followed by species which are all in
lowercase.
- When typed, all binomial names are in italics.
The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus,
Species
IGCSE Biology Notes 2023/2024 Yvonne Cheong
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1.3 Dichotomous Key
Keys are used to identify organisms based on a series of questions about their features.
The answer is D
IGCSE Biology Notes 2023/2024 Yvonne Cheong
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