Biology 103 - Main points/Questions

1. How do plants keep growing for their entire lives?

2. How do animal cells differentiate?

3. What are tissues?

4. How do organisms support themselves?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 21.2

(a) Fertilized egg

All animals start out as a fertilized egg that undergoes mitosis.

In deuterostomes (?) cells divide at right angles while in protostomes (?) they divide in a spiral pattern

Animal Development• We will focus on two basic strategies for

development seen in two major groups

– Protostomes include arthropods and mollusks

– Deuterostomes include all the chordates

• These groups have several differences in their development we focus on 3

– Cleavage pattern

– Timing of cell specialization

– Fate of blastopore

Eight-cell stage Eight-cell stage

Spiral and determinate Radial and indeterminate

Protostome development(examples: molluscs, arthropods)

Deuterostome development(example: chordates)

(b) Four-cell stage

In mammals these cells can be separated and each will produce a separate identical embryo – deuterostome development

Other organisms (protostomes - like arthropods and mollusks) specialize each cell as it is made. Pull one off and the embryo will not develop.

(c) Early blastula

In many animals in both groups the cells divide and produce a hollow ball of cells called a blastula.

(d) Later blastula

Specific cells on the outside of this ball then “crawl” up inside the hollow space in a process called gastrulation

• During gastrulation cells further specialize into three embryonic tissues– Endoderm – the innermost cells

– Mesoderm – cells in the middle

– Ectoderm – cells that remain on the outside

• This process also creates an opening into the ball called a blastopore

Video: Sea Urchin Embryonic DevelopmentVideo: Sea Urchin Embryonic Development

Zygote

Cleavage

Eight-cell stage

Zygote

Cleavage

Eight-cell stage

Cleavage Blastula

Cross sectionof blastula

Blastocoel

Zygote

Cleavage

Eight-cell stage

Cleavage Blastula

Cross sectionof blastula

Gastrulation

BlastoporeGastrula

Ectoderm

Endoderm

Blastocoel

Protostomes and Deuterostomes• We have seen:

– Cleavage pattern differences, spiral vs. radial

– Timing of cell specialization differences

• The last difference we look at is the fate of the blastopore.

– As the embryo develops the open space inside the gastrula will be the digestive tract – the blastopore will be one of the openings – either the mouth or the anus.

Anus

Protostome development(examples: molluscs,

annelids)

Deuterostome development(examples: echinoderms,

chordates)

Anus

Mouth

Mouth

Digestive tube

(c) Fate of the blastopore

Key

EctodermMesoderm

Endoderm

Mouth develops from blastopore. Anus develops from blastopore.

• As embryos continue to develop tissues continue to specialize

• Each of these 3 embryonic tissues will give rise to numerous tissues/organs in the adult

Section 36.6 in your book – gastrulation video

Hierarchy of Biology:• Tissues are groups of cells with similar

structures/functions

• In humans there are many different tissues that work together to build organs

• Organs working together to perform a task are called organ systems

Tissue of the Day• Connective tissue

– Made up of cells surrounded by large extra-cellular matrix (ECM)

– Often (but not always) includes collagen

– Many types including:

– Loose connective – Bone

– Cartilage – Blood (liquid ECM)

Table 28.3

cartilage cells

collagen

Cartilage

chondrocytes

collagen matrix

Cartilage

central canalbone cells concentric bone matrix

Bone

Support system terminology:

• Internal skeleton

• External skeleton

• Hydrostatic skeleton

• Primary vs. secondary cell wall

• Secondary growth in plants

Skeletal systems in Animals

• Hydrostatic skeleton

– Uses pressurized fluids support organisms

weight

– Lacks strength

– Common example:

• Earthworm

Skeletal systems in Animals

• Exoskeleton – external rigid tissue protects and supports

– Gives a lot of protection but...

– Can be very heavy

– Can interfere with growth

– Examples• Arthropods:

• Mollusks

Adult cicada sheds its

exoskeleton as it outgrows it, forming a new exoskeleton.

Skeletal systems in Animals• Endoskeleton –

– Uses internal rigid tissue to support weight

– Offers less protection but...

– Lighter weight

– Growth is simpler

– Examples -

• Vertebrates

A cat skeleton is a nearly ideal

balance of high strength and low

weight. Cats are adept at surviving

long falls in part because of this

balance.

Heavy Organisms Require Large-Diameter Support Structures - in part to support the

added weight of the skeleton itself

skull

Axial skeleton(blue)

Appendicular skeleton(beige)

mandible

sternum

rib

vertebralcolumn

coccyx(tailbone)

clavicle

scapula

humerus

pelvis

ulna

radius

carpals

metacarpalsphalanges

femur

patella

tibia

fibula

tarsals

metatarsals

phalanges

The skeletal system in humans is divided into two parts the axial (in blue here) and the appendicular (in tan) skeletons

skull

Axial skeleton(blue)

Appendicular skeleton(beige)

mandible

sternum

rib

clavicle

scapula

humerus

vertebralcolumn

coccyx(tailbone)

pelvis

ulna

radius

carpals

metacarpals

phalangesfemur

patella

tibia

fibula

tarsals

metatarsals

phalanges

How does the Vertebrate Skeleton develop?

• Bone and cartilage develop from mesodermal tissue

• Bone replaces cartilage during development

bone

cartilage

In this human fetus much of the skeleton is still cartilage - which will be replaced by bone as the fetus ages.

Connecting microscopic view to macroscopic view

• Remember what bone tissue looks like - where do you find tissue like this in your body?

• What do bones look like?

(b)

compactbone

osteon

osteocytes(within spaces)

capillary

central canal

Fig. 28.5

• Notice that there is blood flow in living bone! (Its alive!)

• This is crucial for bone growth & healing.

large blood clot

compactbone

spongybone

1

The Vertebrate Skeleton is alive!

• Notice several types of tissue are actually present in a living bone– Bone– blood– connective tissue and epithelial tissue building

membranes

new bloodvessels

callus ofcartilage and bonereplaces clot

2

bony callus

3

healed fracture

4

periosteum

large blood clot

compactbone

spongybone

new bloodvessels

callus ofcartilageand bonereplaces clot bony callus healed fracture

1 2 3 4

Bone healing is only one way that your body modifies its skeleton