life sciences lesson 1
TRANSCRIPT
LIFE SCIENCESMS NF MDLULI
GRADE 10
LESSON: 1
BIODIVERSITY OF ANIMALS
( UNDERSTANDING LIFE SCIENCES, CHAPTER 12, P342)
Introduction
The animal kingdom extends far beyond humans and other animals we may encounter
1.3 million living species of animals have been identified
Invertebrates (animals that lack a backbone) account for 95% of known animal species.
EARLY EMBRYONIC DEVELOPMENT IN ANIMALS
Most animals reproduce sexually, with the diploid stage usually dominating the life cycle
After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage
Cleavage leads to formation of a blastula The blastula undergoes gastrulation,
forming a gastrula with different layers of embryonic tissues.
EARLY EMBRYONIC DEVELOPMENT IN ANIMALS
Zygote
Eight-cell stage
EARLY EMBRYONIC DEVELOPMENT IN ANIMALS
ZygoteEight-cell stage
Cross sectionof blastula
Blastocoel
Cleavage
Blastula
EARLY EMBRYONIC DEVELOPMENT IN ANIMALS
Many animals have at least one larval stage.
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis.
2. RELATIONSHIP BETWEEN BODY PLAN AND GROUPING OF ANIMALS IN PHYLA
Zoologists sometimes categorize animals according to a body plan.
A body plan is a set of morphological and developmental traits, integrated into a functional whole living animal.
CHARACTERISTICS WHICH EXPLAIN BODY PLAN
Symmetry Cephalization Tissues) Body cavities Protostome and Deuterostome
development
A. SYMMETRY
Animals can be categorized according to the symmetry of their bodies, or lack of it
Some animals have radial symmetry Two-sided symmetry is called bilateral
symmetry
Bilaterally symmetrical animals have:
A dorsal (top) side and a ventral (bottom) side
A right and left side Anterior (head) and posterior (tail) ends
B. Cephalization
Cephalization, the development of a head
C. Tissues
Animal body plans also vary according to the organization of the animal’s tissues
Tissues are collections of specialized cells During development, three germ layers
give rise to the tissues and organs of the animal embryo
GERM LAYERS ARE:
Ectoderm is the germ layer covering the embryo’s surface
Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron
Mesoderm: middle layer of some body plans
Diploblastic animals have ectoderm and endoderm
Triploblastic animals have an ectoderm, endoderm and intervening mesoderm layer.
D. BODY CAVITIES
Most triploblastic animals possess a body cavity A true body cavity is called a coelom and is
derived from mesoderm Coelomates are animals that possess a true
coelom A pseudocoelom is a body cavity derived from
the mesoderm and endoderm Triploblastic animals that possess a
pseudocoelom are called pseudocoelomates Triploblastic animals that lack a body cavity are
called acoelomates
E. Protostome and Deuterostome development
Based on early development, many animals can be categorized as having protostome development or deuterostome development
These two types of developments differ in regard to:
Different cleavage Different coelom formation Fate of the blastop
CLEAVAGE
In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate
With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo
COELOM FORMATION
In protostome development, the splitting of solid masses of mesoderm forms the coelom.
In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom.
FATE OF THE BLASTOPORE
The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula
In protostome development, the blastopore becomes the mouth
In deuterostome development, the blastopore becomes the anus
3. SYNOPTIC CLASSIFICATION OF THE ANIMAL KINGDOM
Kingdom: Animalia Branch 1: Mesozoa (fish parasites)
Branch 2: Parazoa (cellular) Phylum: Porifera (sponges)
Branch 3: Eumetazoa (multicellular)
Grade 1: Radiata (Radial symmetry, tissue level)
Phylum: Cnidaria hydras corals sea-anemones
Grade 2: Bilateria (Bilateral symmetry, organ level,
cephalisation)
Grade 2: Bilateria (Bilateral symmetry, organ level, cephalisation)
Division 1: Protostomia Division 2: Deuterostomia
Division 1: Protostomia
Group 1: Acoelomata (no body cavity) Phylum: Platyhelminthes (flat worms) Group 2: Pseudocoelomata (pseudo body
cavity) Phylum: Nematoda (round worms) Group 3: Eucoelomata Phylum: Annelida (earthworms, leeches:
Metamerism) Phylum: Arthropoda (crabs, insects:
Tagmatisation) Phylum: Mollusca (slugs, snails)
Division 2: Deuterostom
Phylum: Echinodermata sea stars seaurchins
Phylum: Chordata (vertebrates)
Phylum: Porifera (sponges)
Sedentary animals (fixed in one position) They live in both fresh and marine waters Cellular level of development Lack true tissues and organs Asymmetrical
Phylum:Cnidaria (Hydra, sea anemones)
True tissue – Eumetazoa Both sessile and motile forms including
jellies, corals, and hydras Diploblastic body plan Radial symmetry The basic body plan of a cnidarian is a
sac with a central digestive compartment, the gastrovascular cavity
A single opening functions as mouth and anus
Carnivores that use tentacles to capture prey
The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey
Nematocysts are specialized organelles within cnidocytes that eject a stinging thread.
Phylum: Platyhelminthes (flat worms)
Live in marine, freshwater, and damp terrestrial habitats.
Triploblastic development Acoelomates Flattened dorsoventrally and have a
gastrovascular cavity Gas exchange takes place across the
surface Protonephridia regulate the osmotic
balance
Phylum: Nematoda (round worms)
Found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals
They have an alimentary canal, but lack a circulatory system
Sexual Reproduction Internal fertilization Some species are parasites of plants and
animals.
Phylum: Annelida (earthworms, leeches)
Bodies composed of a series of fused rings or compartments - Metamerism
Phylum: Arthropoda (crabs, insects)
Found in nearly all habitats of the biosphere The arthropod body plan consists of a segmented body, hard exoskeleton (made of layers of
protein and the polysaccharide chitin jointed appendages The body is completely covered by the cuticle When it grows, it molts its exoskeleton. Includes: insects, crabs, spiders, millipedes,
centipedes, mites
Phylum: Chordata (vertebrates)
Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates
Vertebrates are a subphylum within the phylum Chordata
Chordates are bilaterian animals that belong to the Deuterostomia.
All chordates share a set of derived characters
Some species have some of these traits only during embryonic development
Four key characteristics of chordates
Notochord Dorsal, hollow nerve cord Pharyngeal slits or clefts Muscular, post-anal tail
EXAMPLES OF CORDATES
ASSESSMENT ACTIVITY
The online test that you have to do is found on: http://goo.gl/YFJXB
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