2023 / 2024 Senior Secondary Biology Field Trip

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Online Learning Platform for Biology Field Study

www.moodle.hokoon.edu.hk

HKNEAC opens an online learning platform account for teachers and students participating in the course. Before participating in the course, students may log in to the platform to learn more about relevant knowledge, concepts, and skills, and complete the quizzes. The platform will automatically record the learning progress and scores of each student so that teachers can keep track of the learning situation of each student.

 

Depending on the needs of teachers and students, teachers participating in the courses may choose from the following learning methods:

  • Watch the video clips and collect data (students learn by themselves without the restriction of time and space)
  • ZOOM live-streaming (collecting data during the field trip, performing statistical analysis, or conducting report review as scheduled)
  • Face to Face Courses (half-day field trip within HKNEAC or 1~3-day field trip off campus)

 Topics for Half-day Courses inside Ho Koon Centre:

  1. The symbiotic world
  2. Exploring microhabitats
  3. Big secret of the cow dung microhabitat
  4. Electron microscope eco-exploration
  5. Microscope eco-exploration
  6. Interesting ecology in the litter

Other Conventional Habitat-Focused Topics:

  1. Study of a freshwater stream ecosystem
  2. Study of mangrove ecosystem
  3. Study of rocky shore ecosystem
  4. Study of sand flat ecosystem


向日葵的頭狀花序

二零二三年六月 第二期

向日葵的頭狀花序

進入正文前,筆者先問各位讀者一條問題:「圖中到㡳有多少朵花?」


圖一:向日葵

相信大家都會直接回答:「一朵。」這個答案不是全錯,但也稱不上全對,為何?

事實上,向日葵並不完全是一朵花,而是由多朵小花組成的。在生物學中,花朵的排列方式稱為花序。花朵有很多種排列方式,例如總狀花序、傘房花序、隱頭花序等。向日葵的小花排列為頭狀花序,即形容花軸(小花著生的位置)縮短成盤狀,上面生長多朵小花。

向日葵共有兩種小花,分別為管狀花和舌狀花:外圍黃色片狀結構是舌狀花的花瓣,而中心黑色的每一點則是一朵管狀花。將向日葵帶進實驗室解剖,我們就能更清楚地觀察小花的組成和排列方式。用刀把花朵縱向切開後,我們可看見中心的管狀結構就是管狀花,開花次序由外而內,換言之愈近外圍的小花就愈先成熟。至於外圍就是舌狀花,其花瓣是舌頭形,因而得名。


圖二:向日葵縱切面,外圍的小花已盛開,而中心的小花則尚未成熟。


圖三:向日葵縱切面特寫,一朵朵管狀花緊密地著生在盤狀花軸上。


圖四:管狀花(左);舌狀花(右)

在立體顯微鏡(也稱為解剖顯微鏡)下,我們能清楚觀察管狀花的結構:橙黃色像湯匙的是雄蕊、開叉的是雌蕊、像王冠般的結構是花冠、下面白色的部分是子房。再把小花仔細解剖,我們可看見圓筒形的花冠實際上由4-5塊花瓣融合而成,而子房內則藏著一粒胚珠。每一個小花都具有繁殖能力,雄蕊和雌蕊會先後成熟,授粉後子房便會發育成果實,裏面的胚珠成為種子。


圖五:管狀花的結構,放大倍數6.7倍。
1: 雌蕊;2: 雄蕊;3: 花冠,由5塊花瓣融合而成;4: 子房


圖六:管狀花縱切面,放大倍數10倍。子房內藏有一粒胚珠(紅圈示),將來會發育成種子。

除了向日葵外,還有不少花朵的排列都是頭狀花序,你能在日常生活中找到例子嗎?

生物科
詹愷盈老師