女拔學生一樣不懂的DSE Biology分高下關鍵題(一)

04/10/2017

我的DSE Biology學生們, 程度最高的高至女拔萃, 其實不明白的地方, 不懂做的題目, 和所有一般學生都是一樣的! 我都可以逐個topics背出來了. 然而他們最不同的是, 他們有堅毅不放棄的精神, 及千方百計找最好的補習老師去幫助自己. 這個系列我作為Biology tutor (包括IB Biology tutor, AQA Biology tutor等等) 希望透過自己補習的經驗, 用例子去演繹DSE Biology by topics的失分之最, 及讓大家以考試為本的方式掌握學習重點, 並能輕鬆明白最艱難的部分, 及大幅縮短溫習時間! 今次我選取了其中一個學生容易混淆和感到難以掌握的其中一個DSE Biology topic – Movement by Humans從HKCEE到DSE Biology, 這一個單元考最多的, 尤其是考MC, 就是movement in elbow joint及movement of the legs at hip joint. 你會常常見到以下兩幅很熟悉的圖:

然後便會有人擺出各種姿勢, 再問你在這個pose的情況下, 哪條muscle是flexor/extensor, 又話者哪條muscle is contracted/relaxed. 這個部分其實十分抵讀, 因為它是一理通, 百理明, 常常考一但要記的資料卻又不多. 我們先來溫習一下concepts of this section

A. Opposing muscle pairs

A. Skeletal muscles always work in pairs so called opposing muscle pairs (antagonistic muscles)
B. When one of the two opposing muscle pairs contract, the other must relax at the same time

B. Identify flexor and extensor

1. One of the opposing muscle pairs acts as a flexor and the other as an extensor
2. When the flexor contracts it bends a limb (move two limb bones together)
3. When the extensor contracts it straightens a limb (move the two limb bones away

然後再將呢兩個concepts套用在Movement at elbow joint and hip joint

C. Movement at elbow joint

i. Movement is achieved by a pair of antagonistic (opposite) muscles - biceps and triceps

ii. Biceps (attach to two tendons) and triceps (attach to three tendons) hence work at opposite directions to bring about the raising and lowering of the forearm

iii. Biceps contracts + triceps relaxes > arm is bent at the elbow joint > forearm is raised

iv. Biceps is therefore a flexor to bend the limb

v. Triceps contracts + biceps relaxes > arm is straightened at the elbow joint > forearm is lowered

vi. Triceps is therefore an extensor to straighten the limb

大家可以咁睇: Tendon在膊頭係用來固定muscle既, 然後另一邊既tendon就可以在muscle contraction既時候, 分別由bicep拉起上面條骨令手提起, 及由tricep拉落下面條骨令手下垂. 永遠留意tendon所拉的是哪條骨, 然後muscle contraction之後條骨會點擺, 下面係幾條例子俾大家應用下: