Friday, 8 May 2020

Chapter 6: Movement (Hydrostatic skeleton and the function of endoskeleton)

Content standard:
Support, movement and growth in animals

Learning standard:
Relate hydrostatic skeleton with movement
Elaborate the function of endoskeleton in animals

Lesson activity:
Welcome back! Today we are going to learn how hydrostatic skeleton bring about movement and the function of endoskeleton in animals.So first, let's talk about hydrostatic skeleton. Do you still remember examples of animals that have hydrostatic skeleton?If you did the previous exercise (powerpoint presentation), i believe you still remember. So, before we discuss about the movement of hydrostatic skeleton, let's watch this video.


In earthworms, the skeleton consists of pressurized fluid within a cavity in the body known as the coelom. The coelom extends throughout the body and is separated into many segments. Although the segments are interconnected, the worm is able to move them independently.Surrounding the fluid-filled coelom are two sets of muscles. Circular muscles wrap around each segment, and longitudinal muscles extend across the length of the body. These muscles are powerful and well-developed. The circular and longitudinal muscles work together to help the earthworm writhe, wiggle and push its way through the substratum of soil.Worms are also covered in short, bristly hairs called chaetae. The chaetae are normally held inside the earthworm's body, but they are extended when the worm is burrowing or anchoring itself in the soil. These chaetae act as an anchor so that the worms can then pull the rear part of their bodies forward. Diagram below shows how the earthworms look like when longitudinal muscles and circular muscles contract.
Diagram 1: The longitudinal muscles and circular muscles
Diagram 2: The "must have" parts in earthworms to able them to move.
Ok. Watch this video to understand more the movement of earthworm.


Next, let's discuss the function of endoskeleton in vertebrates animals. The endoskeleton of vertebrates is an internal scaffolding to which muscles attach and against which they can pull. Vertebrates animals can be divided into three which are land vertebrates, aquatic vertebrates and birds. The function of the endoskeleton in each vertebrates are different depending on their habitat. The entire body of land vertebrates is supported by the endoskeleton. So they have large and strong skeletons.Land vertebrates have a long column of backbone, strong and big pectoral and pelvic girdles to support their body weight. Aquatic vertebrates have very small and weak pectoral and pelvic girdles. A large part of their body is supported by the buoyancy of water. Buoyancy is force from water which allows an object to float. 
Diagram 3: The pectoral and pelvic girdle in two different vertebrates.
Birds have hollow bones to enable them to fly. Advantages of hollow bones are light and strong, allow vertebrates to move faster, and require less calcium and phosphorus. That is why  birds can move faster than the land vertebrates. Now watch this video.


Diagram 4: The comparison between land vertebrates and aquatic vertebrates
Thank you for your participation in today's lesson. Please complete the exercise below.
Exercise:
Click this link below to do the exercise:

References:



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Wednesday, 6 May 2020

Chapter 6: Movement (Size of exoskeleton with growth)

Content standard:
Support, movement and growth in animals

Learning standard:
Relate the size of exoskeleton with growth

Lesson activity:
Hello everyone! How are you? Today we are going to learn about the growth of exoskeleton animal. Do you still remember what you have learnt in the last lesson? You have learnt that exoskeleton animals can grow in size. However, the way they grow are different from other organisms.
Diagram 1: Examples of exoskeleton animals
First let us discuss the meaning of growth. Growth can be described as irreversible increase in body size, mass and number of cells in an organism. Growth in multicellular organism can be measured using parameters like length, height, volume, dry mass and fresh mass over a certain period of time. Basically, the growth curve for most organisms is sigmoid curve or S-shape. The graph below shows example of human growth curve in sigmoid curve or S-shape.
Diagram 2: Growth curve of human
Now let us discuss the growth curve of an insect. It is not the same as human or other organisms growth curve. Why? Because their skeleton are outside their body and they need to remove their exoskeleton in order for them to grow in size. When the length of insects is plotted against the time, it shows very unusual, intermittent growth. The graph has a staircase shape.
Diagram 3: Growth curve of insect (exoskeleton animal)

The horizontal part indicate zero growth. It correspond to the time when the insects stop growing. The five vertical lines of curve are sudden growth spurts. This correspond to the time when the insects (nymphs) cast away their old external skeleton. This process is called moulting(menyalin kulit) or ecdysis.


Diagram 4: The moulting process of grasshopper

Ecdysis takes place each time it grows, right until it reaches the adult stage. During ecdysis, the old cuticle softens and a new exoskeleton forms below it. The old cuticle is then removed. The insects then swallows and retains air to inflate the new soft cuticle until it hardens. Before the new exoskeleton hardens, growth takes place actively to increase the size of the insect.This active growth during each ecdysis gives rise to the growth curve in the shape of a staircase. The diagram below shows the life cycle of an insects. e.g grasshopper.
Diagram 5: The lifecycle of grasshopper
Before we end the class today, let's watch this video.

Thank you for taking part in today's lesson. Make sure to submit your exercise today in WhatsApp group before 4pm. The exercise as below:

Exercise:
1. Draw the growth curve of an insect in an A4 paper.
2. Why does the growth curve of insects has a staircase shape?
3. Explain the metamorphosis (moulting) process of grasshopper based on the growth curve that you have drawn.

 References:

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