1. HKDSE Biology – Biodiversity
Biodiversity
● Refers to the existence of a great variety of life forms in the planet Earth
7 Characteristics of Living Organisms
● Living organisms should have all the 7 characteristics in certain stages of
life
1. Nutrition Organisms take in food for energy and to maintain life
2. Irritability Organisms react to changes in their environment
3. Respiration Organisms break down food in their cells to supply energy for
body activities
4. Growth Organisms increase in size and complexity
5. Movement Animals move from place to place using legs, wings or fins.
Plants generally move by growing
6. Reproduction Organisms produce offspring
7. Excretion Organisms remove waste products produced from chemical
reactions inside bodies
By Michael Ho~* 1

2. HKDSE Biology – Biodiversity
Cell Type
● Cells can be divided into 2 types (prokaryotic and eukaryotic cell)
 Prokaryotes:
Organisms having prokaryotic cells, e.g. bacteria
 Eukaryotes:
Organisms having eukaryotic cells, e.g. fungi, plants, animals
Features Prokaryotic cell Eukaryotic cell
Nucleus - No true nucleus - True nucleus 
- No nuclear envelope - Nuclear envelope 
Genetic material - A single circular DNA - DNA associated with
lying free in cytoplasm proteins forming
chromosomes in nucleus
Membrane bounded
organelles
 
Cell membrane
 
Size Smaller Larger
By Michael Ho~* 2

3. HKDSE Biology – Biodiversity
Classification of Organisms
● Separate organisms into different groups based on their features
● All organisms on Earth are classified into 3 domains and 6 kingdoms
(A) Classifying Organisms
Classification levels Amounts of organisms Similarities among organisms
The most The least
Domain 域
Kingdom 界 ︽
Phylum 門 ︾
Class 綱 ︽
Order 目 ︾
Family 科
Genus 屬
︾
︽
The least The most
Species 種
Species - A group of organisms that can interbreed to produce fertile offspring
(B) Naming of Organisms
● Each species has a scientific name consisting of 2 words
● The 1st word is the name of genus, the 2nd word is the name of species;
separated by space
● The 1st letter of the first word being capital, the rest all being small
● Underlined if written
Students should know the scientific name of modern human
 Homo sapiens (Don't underline the space!)
By Michael Ho~* 3

4. HKDSE Biology – Biodiversity
3 Domains (Bacteria, Archaea, Eukarya)
Prokaryotes Eukaryotes
Domain Bacteria Archaea Eukarya
Kingdom Eubacteria Archaebacteria Protista Fungi Plantae Animalia
Phylum - - - - - -
Class - - - - - -
Order - - - - - -
Family - - - - - -
Genus - - - - - -
Species - - - - - -
Domain Bacteria and Archaea
● Bacteria domain has 1 kingdom, Eubacteria.
● Archaea domain has 1 kingdom, Archaebacteria.
Similarity between Bacteria and Archaea
● They are prokaryotes
Nucleus - No true nucleus
- No nuclear envelope
Genetic material - A single circular DNA lying free in cytoplasm
Membrane bounded
organelles

Cell membrane 
Size Smaller
● Unicellular (Each organism contains only 1 cell)
● Different shapes (rod, spherical, spiral shape)
● Different methods to obtain nutrients
 by photosynthesis (use sunlight to make food)
By Michael Ho~* 4

5. HKDSE Biology – Biodiversity
 by chemosynthesis (use minerals to make food)
 parasitic 寄生 (live in/on other organisms' bodies)
 saprophytic 腐生 (depend on dead organic compounds)
Differences between Bacteria and Archaea
Domain: Bacteria Domain: Archaea
(Kingdom: Eubacteria) (Kingdom: Archaebacteria)
Larger Smaller
Cell membrane is made of lipids Cell membrane is made of lipids (different
structure than those in all other organisms)
(similar to those of eukaryotes)
Cell wall made of peptidoglycan Cell wall contains no peptidoglycan
Ribosomes more different from Ribosomes resemble more closely to
eukaryotes eukaryotes
Live in a wide variety of habitats Live in extreme environments
Example:
 Hot springs (very hot)
 Salt lakes (very salty)
 Acid mine drainage (very acidic)
 Deep ocean floor (anaerobic condition)
By Michael Ho~* 5

6. HKDSE Biology – Biodiversity
Domain Eukarya
● This domain has 4 kingdoms (1.Protista, 2.Fungi, 3.Plantae, 4.Animalia).
● They are eukaryotes with nucleus and membrane bounded organelles.
1. Kingdom Protista
 Most are unicellular; if multicellular, lack differentiation
 2 types of Protista: Algae (autotrophic) and Protozoans (heterotrophic)
(A) Algae (B) Protozoans
 Varies from single cells, colonies,  Unicellular
filaments to sheet-like forms
 Autotrophic nutrition All 3 types of heterotrophic nutrition
Contain chlorophylls and carry out 1. Holozoic
photosynthesis in chloroplasts
-Mobile (∵pseudopodia, flagella, cilia)
-Feed on bacteria, yeast or protozoans
2. Parasitic
3. Saprophytic
 Presence of cell wall made of  No cell wall
cellulose
 Most are aquatic  Live in freshwater or marine, in damp
soil or in plants and animals
 Some unicellular algae may live in
soil or associate fungi to form
lichens
 E.g. seaweeds  E.g. amoeba
2. Kingdom Fungi
 Unicellular/Multicellular
 Heterotrophs: saprophytic, parasitic
 Presence of rigid cell wall made of chitin
 Body is made up of a network of hyphae
 No roots, stems, leaves or chlorophyll
 Use spores for asexual reproduction
 Live in damp places
 E.g. yeast (unicellular), mould and mushroom (multicellular)
By Michael Ho~* 6

7. HKDSE Biology – Biodiversity
3. Kingdom Plantae
 Plants are divided into non-vascular plants and vascular plants
 Autotrophic nutrition:
Contain chlorophylls and carry out photosynthesis in chloroplasts
 Presence of cell wall made of cellulose
Non-vascular plants
Major group Characteristics
Mosses  There is no vascular tissues
 Possess simple leaves and stems
 No true roots but possess rhizoids
for anchoring, absorption of water
and minerals
 Asexual reproduction by spores
 Lack cuticle so restricted to damp,
shady areas
Vascular plants
 With vascular tissue
 Have true roots, stems and leaves
 Have vascular tissues for transport of water, mineral salts and soluble
food substances
 Cuticle on leaf surface to reduce water loss
Major group Characteristics
Ferns  Asexual reproduction by spores
which are stored in sporangia
 Sporangia are located on the
undersurface of the leaf
By Michael Ho~* 7

8. HKDSE Biology – Biodiversity
Major group Characteristics
Gymnosperms  They are trees with needle-shaped
leaves
 Seeds are not enclosed in ovary
and hence not enclosed in fruits
 Naked seeds are protected by
seed coat
They are found in cones
Angiosperms  Seeds are enclosed, protected and
dispersed in ovary and hence
enclosed in fruits
 Possess flowers
 2 types of angiosperms:
Monocotyledons and Dicotyledons
Summary of Kingdom Plantae
Non-flowering plants Flowering plants
Mosses Ferns Gymnosperms Monocotyledons Dicotyledons
Possess simple Possess leaves, stems and true roots
leaves and stems Large leaves Usually needle- Leaves with Leaves with
and rhizoids subdivided into shaped leaves veins in parallel veins in
leaflets network
No vascular Possess vascular tissues
tissues
Reproduce by spores Reproduce by seeds
No cone Possess cone No cone
No flower/fruit Possess flowers/fruits
No cuticle Possess cuticle
Terrestrial Terrestrial (can live in dry places)
(wet area only)
4. Kingdom Animalia
• Multicellular organisms
By Michael Ho~* 8

9. HKDSE Biology – Biodiversity
• Compose of eukaryotic cells without cell wall and chloroplasts
• Animals are divided into invertebrates and vertebrates
1) Invertebrates
⇒ Usually restricted body size as they lack supporting vertebral
columns
⇒ E.g. Jellyfish 水母 , Tapeworms 絛蟲 , Earthworms 蚯蚓 , Snails 蝸牛 ,
Sea urchin 海膽, Insects 昆蟲
2) Vertebrates
⇒ Divided into 5 groups:
(A) fish, (B) amphibians, (C) reptiles,(D) birds, (E) mammals
(A) Fish
 Skin is covered with slimy scales
 Gills present for gas exchange in both larvae stage and adult
stage
 Present of fins for balance and movement
- External fertilization
- Lay eggs in water
- Poikilotherms
Students should realize that sea horses 海馬 (have gills) are fish.
(B) Amphibians
 Skin is covered with moist naked skin
 Present of gills in larvae stage; lungs and skin surface in adult
stage for gas exchange
- External fertilization
- Lay eggs in water
- Poikilotherms
Students should realize that salamanders 蠑螈 (have moist naked skin)
are amphibians.
By Michael Ho~* 9

10. HKDSE Biology – Biodiversity
(C) Reptiles
 Dry skin is covered with hard scales
- Present of lungs for gas exchange
- Internal fertilization
- Lay eggs with hard shells on land
- Poikilotherms
Students should realize that crocodiles 鱷魚 (have dry hard scales) are
reptiles.
(D) Birds
 Body is covered with feathers
 Present of beak
- Present of wing for flying
- Present of dry scales on their legs
- Present of lungs for gas exchange
- Internal fertilization
- Lay eggs with hard shells on land
- Homoiotherms
- Parental care is highly developed
Students should realize that penguins 企 鵝 (have beak and no
mammary gland) are birds.
(E) Mammals
 Skin is covered with hairs
 Present of mammary glands to feed young
 Young develops in uterus
(EXCEPT platypus 鴨嘴獸, spiny ant eater 食蟻獸- lay eggs)
 Present of diaphragm
- Present of lungs for gas exchange
- Internal fertilization
- Homoiotherms
- Parental care is highly developed
Students should realize that bats 蝙蝠 (have hair), whales 鯨魚 (have
mammary gland), dolphins 海豚 (have mammary gland) are mammals.
By Michael Ho~* 10

11. HKDSE Biology – Biodiversity
Summary of Kingdom Animalia
Invertebrates Vertebrates
No backbone Possess backbone
Fish Amphibians Reptiles Birds Mammals
Unique Unique Unique Unique Unique
features: features: features: features: features:
-Slimy scales -Moist naked -Dry scales -Feathers -Hair
-Gills skin -Beak -Mammary
-Fins -GillsLungs glands
-Uterus
-Pinnae
-Diaphragm
Live in water Live in water Most live on land
and on land
(aqueous)
External fertilization Internal fertilization
Egg-laying Born alive
Eggs without shell Eggs with shells No eggs
Poikilotherm Homoiotherm
Dichotomous Key 二叉式檢索表
• Key is a tool for identifying organisms
• Done by sorting organisms into smaller groups according to their characteristics
• Dichotomous key is the one commonly used, providing 2 alternative features at
each step
• The key can be presented in 2 forms (sentence form and chart form)
By Michael Ho~* 11