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23.1 Animal Characteristics
KEY CONCEPT Animals are diverse but share common characteristics.
23.1 Animal Characteristics
Animals are the most physically diverse kingdom of organisms.
• Animals range in size from 25-meter-long blue whales to microscopic rotifers.
• Animals are found nearly everywhere on Earth.
23.1 Animal Characteristics
All animals share a set of characteristics.
• All animals share a unique set of derivedcharacters.
• Animal cells aresupported by collagen. – three-stranded
protein– found in bone,
skin, ligaments,fingernails,and hair
23.1 Animal Characteristics
– diploid parents produce diploid offspring
• Animals are diploid and usually reproduce sexually.
Diploid cells have two copies of each chromosome: one copy from the mother and one from the father
– do not have free-living haploid life stages
23.1 Animal Characteristics
– Homeotic genes control early development.– Hox genes determine the position of cells differentiation.– A Hox gene mutation leads to the development of a body
structure in the wrong position.
• Most animals have Hox genes.
23.1 Animal Characteristics
• Differences in body plans result from differences in the expression of Hox genes.– Hox genes tell embryonic cells which body part to
become. – Mutations in Hox genes led to the vast diversity of
animal species.
head tail
headtail
fruit fly genes
human HOX-B genes
23.1 Animal Characteristics
Each animal phylum has a unique body plan.
• Vertebrates have an internal segmented backbone.• Invertebrates do not have a backbone.• Invertebrates encompass most animal groups.
23.1 Animal Characteristics
Animals are grouped using a variety of criteria.
• Three criteria are used to categorize animals. – body plan symmetry– tissue layers – developmental patterns
gastrovascular cavity
mouth
mesoglea
oral arms
tentacles
blood vessels
brain
hearts
muscle
segmentnerve cord
mouth
digestive track
23.1 Animal Characteristics
• There are two types of body plan symmetry.– bilateral symmetry: body divides equally along one plane
Animals with bilateral symmetry can be divided equally along only one plane, which splits an animalinto mirror-image sides.
23.1 Animal Characteristics
– radial symmetry: body arranged in circle around a central axis
• There are two types of body plan symmetry.– bilateral symmetry: body divides equally along one plane
Animals with radial symmetry have body parts arranged in a circle around a central axis.
23.1 Animal Characteristics
• Bilateral animals have three distinct layers of tissue; radial animals have only two.– both animal types have
ectoderm and endoderm– bilateral animals have
mesoderm• Animals are divided into two
major groups, the protostomes and the deuterostomes.– Protostomes form mouth-
first, and anus second.– Deuterostomes first form the
anus and then the mouth.
23.1 Animal Characteristics
Germ Layer Tissue
• Endoderm-inner most layer, develops into the linings of the digestive tract and much of the respiratory system
• Mesoderm-middle layer, gives rise to muscles and most internal organs
• Ectoderm-outermost layer, gives rise to nervous system and skin
23.1 Animal Characteristics
23.1 Animal Characteristics
Body Cavities
• Acoelomates- have no coelom, or body cavity• Pseudocoelomates-have a false or partially lined body
cavity with only 1 side being covered with mesoderm• Coelomates-have a true body cavity, both sides of the
body cavity are lined with mesoderm
23.1 Animal Characteristics
23.1 Animal Characteristics
A comparison of structure and genetics reveals the evolutionary history of animals.
• Protostomes and deuterostomes are the two major radiations on the animal phylogenetic tree.
Porifera Cnidaria Platyhelminthes AnnelidaMollusca Nematoda Arthropoda
EchinodermataChordata
RADIALRADIAL
NO TISSUESNO TISSUES
PROTOSTOMES
DUETEROSTOMES
jelly
fish,
cor
al, a
nem
ones
spon
ges
flatw
orm
s
Seg
men
ted
wor
ms
clam
s, s
nails
,oc
topu
ses
roun
dwor
ms
crus
tace
ans,
inse
cts,
spi
ders
sea
star
s,
sea
urch
ins
lanc
elet
s,ve
rteb
rate
s
23.1 Animal Characteristics
• The current organization of the animal kingdom shows some unexpected relationships.
• Technological advancementshelp to clarify evolutionaryrelationships.
23.1 Animal Characteristics
Symmetry Practice